BASIC EVO Description of Module and Communication · personal injury caused by improper handling or...

BASICEVO_BA/V1.62_EN

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smartGAS Mikrosensorik GmbH Hünderstrasse 1 74080 Heilbronn Phone: +49 (0)7131 / 797553-0

Fax.: +49 (0)7131 / 797553-10 [email protected] www.smartgas.eu

BASICEVO

Description of Module and Communication


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Table of contents

Table of contents ......................................................................................................... 2

1. General ............................................................................................................. 4

1.1. For your safety ............................................................................................ 4

1.2. Intended use ............................................................................................... 5

1.3. Loss of warranty / liability / disclaimer ............................................................. 5

2. Installing the BASICEVO .......................................................................................... 6

3. Configuration and characteristics of the terminal pins on the BASICEVO .......................... 8

3.1. Function of the OUT 1 signal (TTL digital output) ................................................ 9

3.2. The LED status display .................................................................................. 11

3.3. Function of the COM signal (communication) ................................................... 12

4. Register assignment of BASICEVO ........................................................................... 13

4.1. Detailed information on the status flags register (Sys_status) ............................. 14

4.2. Detailed information on the unit / scaling of the concentration ............................ 15

5. Communication via Modbus .................................................................................. 17

5.1. Structure of Modbus data telegrams .............................................................. 18

5.2. Structure of UART frames ............................................................................ 19

5.3. Modbus control commands .......................................................................... 20

5.4. Modbus ASCII communication device ............................................................ 24

5.5. Modbus address of the BASICEVO .................................................................. 25

5.6. Signal profile of the Modbus communication (ASCII operating mode) .................. 27

5.7. Calculating the checksum (ASCII smartGAS operating mode) ............................ 28

6. Zero point and end point calibration of the BASICEVO ................................................ 29

6.1. Zero point calibration .................................................................................. 30

6.2. End point calibration .................................................................................... 31

7. Annex .............................................................................................................. 34


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7.1. Mechanical dimensions ............................................................................... 34

7.2. ASICEVO operation on a microcontroller ........................................................... 35

7.3. Operating the BASICEVO on a PC ................................................................... 36

8. Service / legal information ................................................................................... 37


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1. General

The BASICEVO is a refinement of the tried-and-tested smartMODULBASIC that has been created

by improving on many aspects. Thanks to its convenient interfaces, it is quick and easy to

integrate into existing measuring and control systems.

The smartMODULBASIC has advanced to form the BASICEVO as follows:

• Expanded operating voltage range of 3.3 V–6.0 V DC (+/- 5%)

• Status display via 2 LEDs (red/green)

• Upgraded software, powerful processor

• Improved mechanical setup, more aesthetic design

• Modbus ASCII (standard and smartGAS-specific) and RTU protocols supported

The BASICEVO is downwards compatible with the smartMODULBASIC, i.e. it can be readily

integrated into existing gas measuring systems.

Based on the physical measurement method of infrared absorption, it provides the best

conditions for reliable and precise measurements, as well as selectivity.

Its compact design and low maintenance effort make it ideal for use in difficult conditions.

1.1. For your safety

• Before connecting and using the BASICEVO, ensure that you have fully ready and

understood these instructions. Please contact our Service department if you have any

questions or if anything is unclear. Important information is written in red. • Store these instructions or pass them on to the device operator for storage, if

necessary; if you sell this device, pass these instructions on to the purchaser. • When installing and operating the device, you must follow the statutory requirements

and guidelines that relate to this product!


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1.2. Intended use

The BASICEVO is a gas measurement cell with independent measurement capabilities and is

used to determine gas concentrations in accordance with its specifications. It is not suitable for

any other measurement or testing purposes, and must not be used in any other way.

BASICEVO must not be operated in potentially explosive environments or under harsh conditions

(e.g. high, condensing humidity, heavy air flow, in aggressive atmospheres, or outdoors without

a housing)!

Please contact our Service department if you have any questions about this.

1.3. Loss of warranty / liability / disclaimer

Opening the sensor, as well as manipulating or damaging the device will invalidate the

warranty!

The warranty may also be invalidated if aggressive chemicals are used, contamination occurs,

liquids penetrate the device or the instructions in this Description of Module and

Communication are not observed!

smartGAS Mikrosensorik GmbH shall not be liable for consequential loss, property damage or

personal injury caused by improper handling or failing to observe the instructions in the

Description of Module and Communication.

Additional information can be obtained from www.smartgas.eu and/or send us at e-mail to

[email protected].

-All rights reserved/subject to change-

Information updated: 06/2017


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2. Installing the BASICEVO

IMPORTANT: Infrared gas sensors are optical measuring systems. Severe impacts and

vibrations must therefore be avoided!

The BASICEVO has two fastening lugs (Figure 1) on the sides. These fastening lugs enable the

device to be screwed in place by M3 bolts. Use only bolts with a flat seating surface, e.g.

cylinder head bolts to DIN 84, fillister head screws to DIN 7985 or similar, never countersunk

bolts!

Figure 1: Fastening lugs - ∅ 3.2mm

The smartGAS sensors allow for installation on the customer's devices in various positions.

Since the calibration ex factory cannot cover every installation situation and ambient condition,

the zero point needs to be checked after installation and if necessary recalibrated.

In any case we recommend a functional test of every device after final installation in the

customer's application in the course of commissioning.

Instructions for calibration can be found in chapter 6.

The maximum tightening torque for the screws on the sensor is 0.3 Nm. Due to this low

tightening torque, it is advisable to use a liquid thread locker such as "Loctite 243" (medium

strength) or self-locking nuts (e.g. to DIN 985).

Ensure that hoses suitable for measurement are used. Certain applications generate corrosive

gases that could cause problems with the hose material.


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During installation, make sure no mechanical pressure is exerted on the housing at the

installation location. Furthermore, the BASICEVO must be fastened to an even surface to prevent

the housing from twisting or tilting.

It is essential to ensure that the sensor at the installation location is not exposed to the

following influences: high humidity (condensing), extreme temperature fluctuations,

mechanical loads (e.g. vibrations), dust, dirt.

Under no circumstances may the sensor (or parts thereof) come into contact with water or

other liquids!

If the sensor is to be mounted near to the airflow created by mechanical or natural

ventilation, the module must not be positioned within a strong airflow!

IMPORTANT:

No aggressive cleaning agents or adhesives may be used.

The BASICEVO must not be modified in any way whatsoever.

Under no circumstances may liquid or dirt be allowed to penetrate the inside of the device!

Failure to comply will result in smartGAS Mikrosensorik GmbH rejecting any claim made

under the guarantee or warranty.


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3. Configuration and characteristics of the terminal pins on the

BASICEVO

The BASICEVO is connected to the power supply via a 4-pin connector strip with a grid

dimension of 2mm. The required socket is not supplied as standard with the BASICEVO. It can,

however, be ordered as a separate item.

Figure 3: Pin assignment of the connector strip on the BASICEVO


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Pins

V+/VCC

Supply voltage: 3.3 V–6.0 V DC (+/- 5%)

Current draw (max.): 0.3 A

Power consumption (mean value when VCC = 5 V): 600 mW

GND Ground, reference point for all signals / voltages

COM

Communication cable. The sent and received telegrams conform to the

Modbus ASCII or RTU protocol respectively. Individual registers can be read

from and written to via this pin.

OUT 1

TTL digital out. (active = 0) open-collector output. Ensures communication,

e.g. by means of a µ-controller via TTL signals. The individual states are

described in detail elsewhere.

3.1. Function of the OUT 1 signal (TTL digital output)

The BASICEVO is capable of displaying up to 7 different states via pin OUT 1 (TTL Digital Output).

The table below shows the coding of the states on the OUT1-pin via the pulse width of the TTL

Open Collector signal.

State ∆t active [s]

(voltage value L)

∆t inactive [s]

(voltage value

H)

Device error 3.2 0

Tox. alarm 2.4 0.8

Ex. alarm 2.0 1.2

Inc. alarm 1.6 1.6

Gas primary alarm 1.2 2.0

Gas pre-alarm 0.8 2.4

Everything OK 0 3.2


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The active switching state appears on the open-collector output as a logical 0 or L (LOW).

Inc., Ex. and Tox. are alarm thresholds that can be optionally set and are not part of the

BASICEVO standard design.

When connecting a pull-up resistance of e.g. 2.2kΩ to V+, the voltage curves for the seven

states can be displayed on the oscilloscope. The signals have an amplitude of V+, the

maximum being 30V DC.

The OUT 1 connection is designed as an open-collector connection. It is wired to GND and may

be loaded with a maximum of 30 mA. The voltage must never exceed 30 V DC. An anti-surge

diode must be used when inductive loads are being switched!


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3.2. The LED status display

Located next to the connector strip are two LEDs (green/red) which show the current device

state as per the table below:

Green LED Red LED Device status

off off No operating voltage / device switched off

flashing off Start phase / self-test (approx. 40 seconds)

on off Normal operation

off on System fault Contact Service!

Figure 4: Position of the status LEDs


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3.3. Function of the COM signal (communication)

The BASICEVO has a semi-duplex UART data interface that supplies and evaluates the non-

inverted UART signals. The semi-duplex operation also means that only one communication

signal (COM) is required. The level on the COM cable is between 0 V and +3.3 V. It may

therefore be necessary to include a level adjustment system depending on the communication

partner (master) connected.

The COM connection is designed as an open-collector connection with an internal pull-up of

10 kOhm at 3.3 V. It is wired to GND and may be loaded with a maximum of 30 mA. The voltage

must never exceed 7 V DC. The use of protective resistors, EMC filters, electrical isolation and

other electrical or electronic measures may cause communication problems and must therefore

be carefully considered by specialist personnel.

The protocol used at user level is Modbus ASCII (original or smartGAS-specific) or RTU.

BASICEVO automatically adapts to the communication method. This affects both the baud rate

and the framing. The Modbus dialect used is also detected automatically. BASICEVO essentially

acts as a slave, which means that it waits for contact from a master.

For the automatic communication detection function to work reliably, certain conditions must

be observed:

• Communication no earlier than 100 ms after switching on the BASICEVO.

• To detect communication, the master must send the first data telegram without gaps

in the byte string.

• No change in baud rate, framing or Modbus dialect during operation. If a change is

necessary, you must switch the operating voltage of the BASICEVO off and on again.

• Supported baud rates: 2400, 4800, 9600, 19200 (Modbus standard), 38400, 57600 and

115200.

• Supported framing in Modbus ASCII (original or smartGAS-specific): 7E1 (Modbus

standard), 7E2, 7O1, 7O2, 7N2, 8E1, 8O1, 8N1 and 8N2.

• Supported framing in Modbus RTU: 8E1 (Modbus standard), 8O1, 8N1 and 8N2.

Chapter 5 provides a detailed overview of the communication process.


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4. Register assignment of BASICEVO

The BASICEVO registers available to the user are shown in the following table. There is read

access to all registers but write access to only some, as shown by the table:

Reg.

Address

Register

name

Write Data

type

Function/explanations

0x0003 T_m No signed

number

Internal sensor temperature as reference

point for the temperature error correction in

multiples of 0.1°C.

0x0009 Sys_status No number System status as a bit string. The meaning

of the individual bits is explained later in

this document.

0x000A Concentration No signed

number

Measured concentration value. The

concentration unit and the scaling are

produced together with the unit code.

Calculation example later in this document.

0x0044 Warn_Level Yes signed

number

Indicates the switch value for a gas pre-

alarm. This threshold can be adjusted by

applying the gas. This modulation value is

reduced by one, entered into this register

and can be freely adjusted by the user.

Ox0045 Alarm_Level Yes signed

number

Indicates the switch value for a gas primary

alarm. This threshold can be adjusted by

applying the gas. This modulation value is

reduced by one, entered into this register

and can be freely adjusted by the user.

0x0047 IR_4tagneu Yes number Zero point reference value.

0x004F Unit No number Unit code and scaling factor for the

concentration. Details and calculation

example later in this document.

0x0054 Span Yes number End point reference value.

0x0080-

0x0083

DeviceType No string Indicates the type of the connected device

0x0084-

0x0085

SW version No string Software version of the connected device


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0x0086-

0x0089

Serial No No string Serial number of the connected device

0x00C0 Modbus_

address

Yes number Modbus address of the BASICEVO. Once this

address has been changed, communication

with the BASICEVO can continue only via the

new address.

The device also has additional registers that are used for diagnostic, setting and calibration

purposes. Write access to registers that are not listed in the table cause the device to function

incorrectly and is therefore forbidden!

4.1. Detailed information on the status flags register (Sys_status)

Status flags register (Sys_status 0x0009)

15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00

Re

serv

ed

Po

we

r_O

n

WD

G_W

arn

EE

P_E

rro

r

MW

_act

ive

To

x

Ex

Inc

MW

_ok

Co

rr

Sta

rtu

p

Wa

rn

Ala

rm

Sys

err

Wa

rmu

p

Te

st

The meaning of the individual status flags, from right to left, is:

Flag 0: Test flag, Value “1” when the self-test has been triggered

Flag 1: Warmup, Value “1” during warm-up phase after the start

(approx. 10 sec)

Flag 2: Syserr, Value “1” in case of a device and/or system error

Flag 3: Alarm, Value “1” in case of gas primary alarm

Flag 4: Warn, Value “1” at the gas pre-alarm

Flag 5: Startup, Value “1” in the start-up phase (approx. 40 sec)

Flag 6: Corr, Value “1” when the correction function is active (always)

Flag 7: MW_ok, Value “1” when the zero point has been set

Flag 8: Inc, Value “1” when inc concentration has been reached

Flag 9: Ex, Value “1” when ex concentration has been reached

Flag 10: Tox Value “1” when Tox concentration has been reached

Flag 11: MW_active, Value “1” when averaging for drift correction is active

Flag 12: EEP_error, Value “1” when EEprom error


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Flag 13: WDG_Warn, Value “1” when watchdog has responded

Flag 14: Power_On, Value “1” when voltage has been switched on

Flag 15: Reserved Always 0

The two flags 6 (Corr) and 7 (MW_ok) are internal flags set in the manufacturing process of the

individual BASICEVO. They are also used for quality control purposes and are set at the value “1”

if the respective BASICEVO has been temperature-compensated and calibrated.

4.2. Detailed information on the unit / scaling of the concentration

The concentration register (0x000A) provides a numeric value that varies in terms of its scaling

and unit depending on the BASICEVO version. The Unit register (0x004F) can be used to correctly

calculate the concentration value. The meaning of the numeric value in the Unit register

(0x004F) is therefore displayed as follows:

Value = 0: Unassigned Reserved for special applications

Value = 1: ppm x 0.01 or ppb x 10

Value = 2: ppm x 0.1 or ppb x 100

Value = 3: ppm x 1 or ppb x 1000

Value = 4: Vol% x 0.001 or ppm x 10



Value = 7: %UEG x 0.01 Lower explosion limit

Value = 8: %UEG x 0.1 Lower explosion limit

ppm stands for 1 x 10-6 volume fraction of the measurement gas in terms of the total gas volume.

ppb stands for 1 x 10-9 volume fraction of the measurement gas in terms of the total gas volume.

Vol% stands for 1 x 10-2 volume fraction of the measurement gas in terms of the total gas

volume. UEG indicates the measurement gas content in the air necessary for there to be an

explosive mixture.


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Example 1:

If the value in the concentration register (0x000A) is 3425 and the value in the unit register

(0x004F) is 2, the correctly scaled concentration provided with the unit is 3425 x (ppm x 0.1) =

342.5 ppm.

Example 2:

If the value in the concentration register (0x000A) is 7236 and the value in the unit register

(0x004F) is 5, the concentration is 7236 x (Vol% x 0.01) = 72.36 Vol%.

The scaling factor and the concentration unit can also be found on the accompanying QA

certificate enclosed with every BASICEVO.


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5. Communication via Modbus

The BASICEVO supports the Modbus protocol in ASCII and RTU mode thanks to its serial semi-

duplex interface. In ASCII mode, in addition to the standard variant, there is a smartGAS-

specific derivative that differs from the standard in terms of the checksum calculation.

Modbus communication fundamentally functions based on a query/response mechanism. A

master sends the query to one of possibly multiple slaves (subscribers). Each connected

subscriber therefore receives a subscriber address that is unique in the network. Only the

subscriber that has found its address in the query from the master will respond.

The type of query is determined by a control command (function code). This can, for example,

be about writing data or reading data to/from the subscriber. Depending on the control

command, there is a data portion for both the query and the response.

Each query and each response must be clearly identified by its beginning and by its end. It will

also be helpful to add a test field to the transported data again so that potential communication

errors can be detected. The Modbus derivatives implement this in different ways.

You can obtain detailed information about the Modbus protocol at www.modbus.org


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5.1. Structure of Modbus data telegrams

The following two tables show the basic structure of an ASCII data telegram and a RTU data

telegram. The tables show that the address, control command and data portion are based on

the same source data for both telegram types:

Dialect Start Address Control Data LRC End

Modbus

ASCII

1 character

':'

2

characters

e.g.:"A0"

2

characters

e.g.:"03"

0 to 2x252 characters

e.g.: "00050002"

2

characters

e.g.:"A6"

2

characters

CR,LF Commu-

nication: 0x3A 0x41, 0x30 0x30, 0x33

0x30, 0x30, 0x30,

0x35

0x30, 0x30,0x30, 0x32

0x41, 0x36 0x0D,

0x0A

Dialect Start Address Control Data CRC End

Modbus

RTU

1 byte

e.g.: 0xA0

1 byte

e.g.: 0x03

0 to 1x252 bytes

e.g.: 0x00, 0x05,

0x00, 0x02

2 bytes,

e.g.:0xA4,

0xD3

Commu-

nication:

Pause,

3.5 char 0xA0 0x03

0x00, 0x05, 0x00,

0x02 0xA4, 0xD3

Pause

3.5 char

In ASCII mode, each 8-bit byte is therefore sent as two ASCII characters. One byte can also be

seen as two nibbles. One nibble has 4 bits and represents precisely one hexadecimal character.

As can be seen in the telegram examples, the result of the byte containing the information

“0xA6” is the two ASCII characters “0x41” = ‘A’ and “0x36” = ‘6’.

In ASCII mode, 7 data bits are sufficient for transporting the characters via the interface. The

ASCII mode has a historical advantage. All Modbus data telegrams can be “read” with a ASCII

terminal; plain text appears on the screen.

In RTU mode, however, each 8-bit byte is handed over unchanged. This inevitably means that

in RTU mode. UART frames with 8 data bits need to be used. The advantage of the RTU mode

lies in the more effective utilisation of the interface because only around half of the data

volume needs to be transmitted compared to the ASCII mode.


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5.2. Structure of UART frames

A UART frame is structured as follows:

Start N data bits Parity M stop

1 start bit (always 0), followed by

7 or 8 data bits, starting with the lowest-value bit,

1 parity bit (optional). If used, the parity bit can be even or odd,

1 or 2 stop bits (always 1).

The nomenclature for describing a UART frame consists of a number, followed by a letter and

ending with a number. The first number denotes the number of data bits contained in the frame.

The following letter describes the type of parity with N for none, E for even and O for odd. The

last number indicates how many stop bits are being sent. The standard specification for Modbus

RTU is 8E1, and 7E1 for Modbus ASCII.

Examples:

8N1 means that 8 data bits are being used, there is no parity (N) and 1 stop bit is being used.

7E1 means that 7 data bits are being used, there is even parity (E) and 1 stop bit is being used.

Furthermore, when transporting a UART frame via the electrical cable, how “quickly” the

transmission occurs is important. The term baud rate is a definition for this. The baud rate

describes how many bits are transmitted per second. Standard baud rates are 2400, 4800, 9600,

19200 (Modbus standard), 38400, 57600 and 115200. All of these are fully supported by BASICEVO.


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5.3. Modbus control commands

Two command codes (function codes) are sufficient for communication with BASICEVO. These

are 0x03 – Read (multiple) holding registers and 0x06 – Write (exactly one) register. One

register is 16 bits wide and therefore consists of 2 bytes:

Register 15 … 0

High order byte – Hi Low order byte – Lo

All the BASICEVO data that the user can access is shown on registers that are each 16 bits wide.

The two control commands will now be explained using some examples.

Control command 0x03 – Read (multiple) holding registers

This control command allows you to read values from the BASICEVO. The main thing is that only

defined registers can be read. This must therefore be checked especially when queries are sent

to multiple registers. Chapter 4 has information on register assignment.

Example 1 – Reading out the 4 registers for “Device Type”:

Request Response Meaning of the data

Field (Hex) Field (Hex)

Control command 03 Control command 03

Hi start address 00 Number of bytes 08

Lo start address 80 Hi register value (128) 53 ‘S’

Number of Hi registers 00 Lo register value (128) 4D ‘M’

Number of Lo registers 04 Hi register value (129) 46

Lo register value (129) 43 ‘C’

Hi register value (130) 4F ‘O’

Lo register value (130) 32 ’2’

Hi register value (131) 20 ‘ ’ = Empty characters

Lo register value (131) 20 ‘ ’ = Empty characters

In this example, 4 registers of the BASICEVO were read starting from register start address

0x0080 (decimal 128). The response consisted of a payload of 8 bytes. This was clearly a CO2

module. The 3 letters SMF mean that it is a BASIC sensor.


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Example 2 – Reading out the “Concentration” register:





Lo start address 0A Hi register value (10) 01 Concentration

is 456 Number of Hi registers 00 Lo register value (10) C8

Number of Lo registers 01

In this example, exactly one register was read starting from register start address 0x000A

(decimal 10). The two data bytes were transmitted combined as a hexadecimal value. If this

value is converted to a decimal number, the result is a concentration of 456.

Example 3 – Reading out the “Unit” register:





Lo start address 4F Hi register value (79) 00 3, means ppm x 1

Number of Hi registers 00 Lo register value (79) 03

Number of Lo registers 01

In this example, exactly one register was read starting from register start address 0x004F

(decimal 79). The two data bytes were transmitted combined as a hexadecimal value. If this

value is converted into a decimal number, the result is 3. This stands for the unit ppm with the

scaling x 1. Combined with the data from examples 1 and 2, the BASICEVO that was read has

therefore measured a gas concentration of 456 ppm CO2.


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Control command 0x06 – Write to (exactly one) register

This command enables a new value to be systematically written to a certain register. However,

it is only possible to write to those registers intended for this purpose. For more information on

this, see register assignment in Chapter 4.

Example 1 – Writing to the “Modbus_address” register:




Hi register address 00 Hi register address 00

Lo register address C0 Lo register address C0

Hi register value 00 Hi register value (192) 00 The new address of

the module (160) Lo register value (192) A0 Lo register value (192) A0

In this example, a new Modbus address for the BASICEVO was set. Once this communication

sequence is complete, the device is only responsive at the new address!

Example 2 – Writing to the “IR_4tagneu” register:





Lo register address 47 Lo register address 47

Hi register value (71) 00 Hi register value (71) 00 The zero point has

been reset (1) Lo register value (71) 01 Lo register value (71) 01

In this example, the zero point BASICEVO has been reset. This was done by writing the value 1 to

register 0x0047 (decimal 71). The device subsequently internally calculated and saved the

current corrected value for the zero point. Reading out the same register then shows the fixed

value of the correction.

The zero point must only be set when zero gas and then a stable concentration value are

applied! You can find more information in Chapter 6.


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Example 3 – Writing to the “Span” register:





Lo register address 54 Lo register address 54

Hi register value (84) 27 Hi register value (84) 27 Span was set to

10000 (presetting) Lo register value 10 Lo register value (84) 10

In this example, a new end point correction for the BASICEVO was set. A value of 10000 means

that the correction factor is 10,000. This is also the delivery condition. A value of 11000 would

mean that the concentration value displayed is 10% higher than internally measured. This

register therefore enables deviations of the BASICEVO in the concentration display to be

corrected. It stands to reason that the current span value is read first so that it is clear how the

new value can be calculated.

The end point must only be set in this way when a suitable test gas and then a stable

concentration value are applied! More information in Chapter 6.

Setting the end point only makes sense if the zero point has previously been set correctly.


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5.4. Modbus ASCII communication device

Figure 5 shows the state diagram of the transmission and receiving devices in principle,

regardless of whether it is master or slave.

Figure 5: State diagram of a Modbus subscriber (ASCII operating mode)

If an incomplete query is sent to the BASICEVO it does not return a response. The module

behaves as if at least one register in the register area being queried does not exist. Error-free

telegrams are processed, others are discarded.

Wait

(ready to send or

receive)

Start

Send

Receive

Send

Send

End

Waiting for

End of telegram

Request

Receive ‘:’ (0x3A)

Receive characters/

Set characters in the

receive buffer

Receive ':' (0x3A)/

Empty receive buffer

Receive CR

(0x0D)

Receive ‘LF’ (0x0A) / check

received telegram (LRC,

parity, slave address, etc.)

Send

’:’ (0x3A)

Send ’CR’,‘LF‘

(0x0D, 0x0A)

Send all

characters

Receive ':' (0x3A)/

Empty receive buffer


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5.5. Modbus address of the BASICEVO

In the examples above, the focus has been on the control commands without mentioning the

scope of the telegram in detail. However, the telegram also includes the address of the slave

subscriber, which is either queried or delivers a response to a query.

With the BASICEVO, the device address as delivered corresponds to the last two digits of the

serial number of the BASICEVO – see Figure 6.

Figure 6: Determining the Modbus address of the BASICEVO as delivered

Figure 7 is a flow diagram that shows how unknown Modbus module addresses can be

determined. Now, any register (e.g. serial number) can be queried via all module addresses (1–

247) with a timeout of one second. If a module is queried with the correct address, it reacts by

sending a response. The module address is included in this response. Thus, at the end of the

search cycle, module responses can be used to analyse which module addresses are presently

connected to the bus system. When querying the serial numbers, it is even possible to conclude

which address is assigned to which module.

The permitted address range for the BASICEVO is between 1 and 247. According to Modbus

specifications, the addresses 248–255 are reserved. Address 0 stands for broadcast.

Please note:

Device address = #35 decimal 0x23 hex

If the serial number ends with “00”,

the address is always #100 decimal =

64 hexadecimal.


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Figure 7: Flow diagram – determining unknown addresses of the modules being used

(Modbus ASCII operating mode)

Connect module

Query telegram for reading out the serial number

: Addr. 03 0086 0004 LRC CRLF

Timeout: = 1s

Addr.: = 1 to 247 STEP 1

Calculate LRC

Timeout

Output serial

no. and address

Send query

Valid response

Addr.=

248?

START

STOP

Y

no

no

no

Y

Y


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5.6. Signal profile of the Modbus communication (ASCII operating

mode)

Figure 8 shows a potential scenario of a data exchange between the master and the connected

subscriber/s (primarily BASICEVO). This assumes a baud rate of 2400 and the Modbus

communication running in ASCII mode. Times vary accordingly for other baud rates.

Figure 8: Time diagram – Data interchange between master and BASICEVO

The duration of a query string is 70–73 ms. A brief pause (max. 400 ms) may then follow. The

module response then follows. This depends on the number of bytes being read out. If only one

byte is read out, the module response is approx. 70 ms. When multiple bytes are being read out,

the response phase is correspondingly longer.

Basically, it can be said that the BASICEVO reacts to a correct query reliably within 400 ms.

The character string is then sent immediately without a response pause.


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5.7. Calculating the checksum (ASCII smartGAS operating mode)

This subchapter explains the calculation of the checksum (LRC) specifically for the ASCII

smartGAS operating mode. How the calculation of the LRC checksum in ASCII standard and

CRC checksum in RTU functions is described thoroughly in the documents of the Modbus

standard. It is helpful to have a conversion table for ASCII values in hexadecimal and decimal

format as follows:

ASCII ’0’ ’1’ ’2’ ’3’ ’4’ ’5’ ’6’ ’7’ ’8’ ’9’ ‘A’ ‘B’ ‘C’ ‘D’ ‘E’ ‘F’

Hex 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46

Dec. 48 49 50 51 52 53 54 55 56 57 65 66 67 68 69 70

The checksum is calculated using the address, the control command and the associated data

after the conversion to ASCII has occurred. By way of example, we generate a query for reading

the concentration register from the BASICEVO with the address 35 (decimal).

Therefore, in hexadecimal format, the resulting byte string is 0x23, 0x03, 0x00, 0x0A, 0x00,

0x01. After the ASCII conversion, the result is the data string 2303000A0001. The data string is

now converted and the checksum is formed:

Address Command Start register Number of registers Sum

ASCII 2 3 0 3 0 0 0 A 0 0 0 1 ---

↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓

Dec. 50 51 48 51 48 48 48 65 48 48 48 49 602

Sum = 602

Checksum = 255 – 602 + 1 = - 346

Modulo sum(256) = - 346 + 256 + 256 = 166 (dez.) → A6 (ASCII hex.)

Putting the starting character at the beginning and the calculated checksum and end code at

the end would mean that the following data string would be sent:

:2303000A0001A6<CR><LF>

The checksum is included each time data is sent and is then recalculated by the recipient again.

If the data set is corrupted or adulterated, the checksum calculated by the recipient would

deviate from that which was sent. The data set would then be unusable.


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6. Zero point and end point calibration of the BASICEVO

The following explanations concern the calibration of the BASICEVO via Modbus (ASCII operating

mode in the smartGAS variant). Examples are used to describe the communication content for

exactly this operating mode. A requirement here is that a corresponding communication partner

is available, ready for operation and connected. The examples refer to a BASICEVO module with

the Modbus address 35 (0x23); the checksums are shown as symbols and can be determined

using the information Chapter 5.7.

To adapt the BASICEVO with the calibration gases, the module box illustrated below can be

obtained:

BASICEVO module box calibration adapter

The BASICEVO must be in operation for 30 minutes before calibration can be done! The

calibration gas concentration (zero and end point) must be stable. This may take a few minutes

depending on the boundary conditions! Unless otherwise specified for the application, we

recommend testing the sensors every 12 months.


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6.1. Zero point calibration

To calibrate the zero point, zero gas must be flowing in the BASICEVO. Furthermore, you must

ensure that the measured concentration value is sufficiently stable. This is achieved by reading

out the concentration register (0x00A) again. If the value fluctuates only by a few digits, the

zero point can be set.

Reading out the concentration register:

Sending the following command to the BASICEVO (checksum in symbols):

“:2303000A0001XX<CR><LF>”

Start Address 35 Read Start register 0x000A Number of registers: 1 Checksum

: 23 03 00 0A 00 01 XX

The following response is sent (the file contents may deviate, checksum in symbols):

“:230302001AYY<CR><LF>”

Start Address 35 Read Number of bytes: 2 Data: 26 Checksum

: 23 03 02 00 1A YY

The content of the concentration register is 26, indicating that it makes sense to set the zero

point. If this value remains stable for a prolonged period, the zero point can be set.

Setting the zero point by writing to the IR_4tagneu register:

This requires the value 1 to be written to the “IR_4tagneu” register (0x0047). For BASICEVO, the

value 1 is the indicator to value the measured concentration as exactly 0.

We strongly recommend that no value other than 1 is written to the register, because this could

shift the zero point significantly!


“:230600470001ZZ<CR><LF>”

Start Address 35 Write Register: 0x0047 Data: 1 Checksum

: 23 06 00 47 00 01 ZZ


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If the command was correctly transmitted, the same command is sent back as a response.

It is now possible to verify that the concentration value is quite close to 0 by querying the

concentration register (0x000A) as described above.

6.2. End point calibration

Setting the end point requires that BASICEVO has an exact zero point as a reference.

We strongly recommend carrying out a zero point calibration as described above before

calibrating the end point.

The concentration of the test gas used for the end point calibration should be between 50% and

100% of the BASICEVO measuring range. Lower concentration test gases could lead to a

significant loss of accuracy. Higher concentration test gases could not be measured exactly.

The end point is determined in the BASICEVO via the “Span” register (0x0054). This register

contains a correction value (presetting 10000) that is used to evaluate the internally measured

concentration. The concentration thus scaled is available in the concentration register already

explained (0x000A).

For the end point calibration to be successful, the “Span” register (0x0054) must be read out

first as a value that does not equal 10000 could already be present.

Reading out the span register:


“:230300540001XX<CR><LF>”

Start Address 35 Read Start register 0x0054 Number of registers: 1 Checksum

: 23 03 00 54 00 01 XX


“:2303022701YY<CR><LF>”


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: 23 03 02 27 01 YY

BASICEVO therefore contains 9985 as the value in span. This value must be noted; we call it

Span_OLD.

To calibrate the end point, test gas of a known concentration must be BASICing in the

BASICEVO. Furthermore, you must ensure that the measured concentration value is sufficiently

stable. This is done by reading out the concentration register (0x00A) again as described for the

zero point calibration. If the value only fluctuates by a few digits, it can be used.

Reading out the concentration register:


“:2303000A0001XX<CR><LF>”

Start Address 35 Read Start register 0x000A Number of registers: 1 Checksum

: 23 03 00 0A 00 01 XX


“:23030203D2YY<CR><LF>”


: 23 03 02 03 D2 YY

The sensor therefore indicates a Conc_OLD concentration of 978. The concentration of the

Conc_CAL test gas is 1003, for example.


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Recalculating the value for span:

Span_NEW = Conc_CAL * Span_OLD / Conc_OLD = 1003 * 9985 / 978 = 10240

Setting the end point by writing to the span register:

To do this, the value 10240 that was just calculated must be written to the “Span” register

(0x0054).


“:230600542800WW<CR><LF>”

Start Address 35 Write Register: 0x0054 Data: 10240 Checksum

: 23 06 00 54 28 00 WW

If the command was correctly transmitted, the same command is sent back as a response.

It is now possible to verify that the concentration value is quite close to the test gas value of

1003 by querying the “Concentration” register (0x000A) as described above.


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7. Annex

7.1. Mechanical dimensions


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7.2. ASICEVO operation on a microcontroller

For the BASICEVO to communicate with a microcontroller, the level of the signals at the module

COM pin must be adapted to the microcontroller. The easiest method is via an RS485 interface

module that must be selected according to the microcontroller voltage supply. The TXD

(transmit data), RXD (receive data) and a signal for activating the TXEN (transmitter enable)

UART signals must be provided at the microcontroller. The following figure shows the circuit:

Figure 9: BASICEVO on a microcontroller

The circuit is designed for a microcontroller with 5 V operating voltage. When operating at 3.3 V,

use a ADM3075 (or equivalent types) rather than the ADM4850 (or equivalent types). All other

components are unaffected.

Up to 16 BASICEVO can be operated in parallel with this circuit. This requires the devices to have

different Modbus addresses.

It should be noted that BASICEVO must be connected to a power supply in addition to the

communication connection shown above.


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7.3. Operating the BASICEVO on a PC

Operating exactly one BASICEVO on a PC requires a special USB adapter incl. software; this can

be purchased from smartGAS as an accessory. The BASICEVO is powered via the USB port; an

additional power supply is not necessary. The following figure shows one such adapter:

Figure 10: USB adapter for operating a BASICEVO on the PC


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8. Service / legal information

Our Service department is your partner at all times. We guarantee you full

satisfaction, expert advice and top quality.

Service and support:

Please contact your distributor or us directly at:

Tel.: +049 7131 / 797553-0 or by e-mail [email protected]

You can also contact us via our website www.smartgas.eu.

Legal information:

smartGAS BASICEVO Description of Module and Communication

© smartGAS Mikrosensorik GmbH

Edition V1.62 / June 2017

The figures and drawings used in this description may differ from the originals;

they are provided solely for illustrative purposes!

All information – including technical specifications – is subject to change

without notice.

smartGAS Mikrosensorik GmbH

Hünderstrasse 1

74080 Heilbronn

Germany

Telephone +49 7131 797553-0

Fax +49 7131 797553-10

www.smartGAS.eu

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