Level Module - DESY€¦ · A 16 bit word will be sent (EPICS data type WAGO_AI2). Bit 15: Sign,...
Transcript of Level Module - DESY€¦ · A 16 bit word will be sent (EPICS data type WAGO_AI2). Bit 15: Sign,...
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Level-Module
The level module can replace some other devices. The main task is the measurement of
helium filling level. Controlling a heater device and caring about a hardware interlock to
protect the heater against burning out is another one. The situation of the coexistence of a
heater and a level meter is quite common. The level module does the task of measuring,
controlling and interaction between these things.
Operation / Installation
The module must be installed on a DIN rail.
At four existing connectors the external
devices are plugged in. These are:
the superconducting Sensor
heater analog control
heater release (contact)
heater temperature sensor (TC)
The module should be mounted in a way that
natural thermic air movement is possible. In
case of horizontal mounting active cooling is
necessary.
The connectors of the level
module are not isolated
relative to the logic and
power supply.
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LEVEL
Status sensor
Status temp.
Heater ON LED Level > Min
LED System/CPU
LED Addressing
Connection to sensor
Thermocouple Type K
Analouge output
Heater Release (Relais contact)
Figure 1: Display and connections of the Level-Module
(no function)
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1 : + U
2 : U
3 : + I
4 : I
1 : + U
2 : U
3 : AGnd
4 : prot. Gnd
1 : AGnd
2 : DC-OK
3 : AGnd
4 : + U
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1
1
2
2
2
3
3
3
4
4
4
Initial-Resistor of
the level sensor
Figure 3: Level module, connection thermocouple at the plug
Figure 4: Level module, connection heater power supply at the plug
Figure 2: Level module, connection superconductive level sensor at the plug
+ at higher temperatures
DC-OK*
not implemented
Junction at room
temperature!
Netzgerät für Heizer
+
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Displays
Every module type has LEDs „SYS“, „ADR“ and more specific ones. SYS is yellow
during initializing. Red indicates an error. Green stands for normal operation.
Yellow/green flashing happens, when the module has been halted by the coupler after the
module has worked normally before. This happens for example if the field bus is
disconnected after having been running already.
These situations can be reasons for error indication:
- The module has a hardware error (i.e. DC/DC converter or ADC).
- The configuration requested by the module doesn’t fit to the existing one.
- The fieldbus at the coupler is not supported by the module.
Errors are read by the coupler and can be sent to the control system.
The ADR LED indicates the status of addressing. Yellow: Address is to be determined,
green: address found, red: conflicting addresses. Only if a correct address could be found
data communication over the internal CAN bus can take place.
The remaining LEDs show the status of the level sensor, the heater and the thermocouple
at the heater. Additionally there is a LED which shows that a minimum of liquid helium
is in the containment.
LED sensor (S)
Green: Normal operation in cold environment.
Green flashing: Sensor is being activated.
Red: Sensor is switched off in warm environment.
Red flashing: Sensor has an error. Check status bits.
Dark: Sensor is switched off.
If measuring has not yet started, green means ‘sensor is OK’. After switching on the
sensor current the LED is flashing green until getting stable level readings. When the
sensor is switched off (since V1.4) it is tested in the beginning and when its plug is
connected. The result is displayed for a second as red (error) or green (ok) light.
LED thermocouple (T)
Blue: Heater is cold enough to be switched on.
Red: Heater is still too warm, no release.
K1
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2
3
4
Figure 5: Level module, connection heater power release at the plug
0V +24V
Line
1 : n.c.
2 : n.c.
3 : Rel Com
4 : Rel. NO
K1
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Red flashing: The thermocouple has an error.
LED thermocouple (T) when simulated (see chapter about DIP-switch)
Blue flashing: Simulation correct. Temperature release permanently granted.
Red flashing: Error.
LED heater (H)
Green: Heater release (relay output) ON.
Dark: Heater OFF.
Green flashing: The relay has an error.
LED filling level (LEV)
Blue: Minimum level reached (a release condition of the heater).
Dark: No filling level release.
How the Filling Level Measurement works
The sensor for measuring the filling level mainly consists of a thin wire which becomes
superconducting at temperatures in a helium bath. For production a niobium titanium
wire (NbTi) is used which has a thin copper layer on the surface. This is good for to be
soldered easily. In contrast to the production of superconducting magnet coils the copper
layer is not desired. In case of a quench this layer shall not take over the current in the
conductor but the relative high resistance of the alloy in normal conducting state is
needed for the measurement principle. Therefor the copper is removed by etching after
soldering. During measurement the wire is mounted vertically in the helium bath. In the
area of helium gas the thermally coupling between the wire and the cold environment is
so bad, that the current through the wire heats it above the transition temperature of about
9 Kelvin. In the fluid the wire keeps cold. In the area of transition the right choice of the
current is important so that the boundary to the superconducting area is just at the surface
of the fluid and that this transition is stable.
If the temperature in the whole containment is lower than the transition temperature, the
whole wire is superconducting. When switching on the current nothing would change
because no heat is dissipated. Therefor a normal resistor is soldered on the upper end of
the wire which heats up and initiates a quench by the thermal contact with the measuring
wire. This quench propagates down until it reaches the surface of the liquid. During the
wire heats up a little in the gas area, the resistance is still going up a little until it is
reaching an equilibrium. The level module considers this by waiting for this equilibrium
in the beginning or after a break in measurement. A quench propagation speed of at least
7.8 inch/second is assumed. As soon as the resistance does not become more between two
measurement cycles the module changes to normal operation. During stabilization the
green sensor-LED is flashing. If this phase ends because of a timeout the LED is flashing
red shortly in the end. During operation this LED is green. If the resistance is bigger as
the resistance of the wire in cold gas, it is assumed that the containment is warm. The
sensor will be switched of and the LED lights red in this case. For this mechanism it is
necessary that the active length and the specific resistance of the wire at 20 K have been
provided correctly. In extreme cases the sensor could be destroyed when the wire is
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loaded in vacuum and the warm state could not be recognized because of wrong
parameters.
Parameterization
The bus master is sending configuration data as well as parameters of the connected
modules over the field bus. At DESY these data are built using the I/O configurator
which has access to the device database. The choices (menus) and default values are
taken out of the GSD file for the ‘Kryo-I/O-System’.
These parameters must be set:
Minimum level for releasing the heater.
Specific resistance of the sensor wire (11.4 /inch AMI standard)
Units of active length (cm or inch)
Sensor operating current (2K-sensors 53.1mA, 4K-sensors 75mA)
Heater analogue control (without, 0..2V, 0..2.5V or 0..4V)
Active sensor length (units as chosen before)
Correction
The correction value is left zero in the beginning. If all parameters are set according to
the data sheet of the manufacturer of the sensor and in cold empty reservoir the level
module does not show 0% the correction can be made. At cold empty tank the level
value is noted. This is our variable h0.
The correction parameter K computes as follows:
K1 = h0 / (100 - h0)
Input of the correction in per mille: K = 1000 * K1
Example: Display value -1.3%
K1 = -1.3 / (100 – (-1.3)) = -0.01283..
K = -0.01283 * 1000 = -13 (rounded to the nearest integer number)
After K has been set as the correction parameter and after rebooting the IOC (fieldbus
master) the level value will show the right value.
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Address and Data Layout The base address results depending on position and type of plugged-in modules (separate
for input and output). The offset addresses of process value positions are organized as
follows:
Inputs (from process):
0: Status sensor (2 byte)
2: Status heater (2 byte)
4: Filling level (2 byte, signed, last 3 bits status, „WAGO_AI2“)
6: Temperature heater (2 byte, last 3 bits status, „WAGO_AI2“)
8: Heater output read-back (2 byte, last 3 bits status, „WAGO_AI2“)
10: Readback of minimum level for heater release (1 byte, UNSIGN8)
Outputs (to process):
0: Command word (2 Byte)
2: Setpoint filling level (2 Byte) (when using internal control, not implemented)
4: Heating power externally commanded (2 Byte)
When using the I/O configurator the user is free of the need to calculate addresses.
Status sensor – meaning of Bits
0: Sensor current flows continuously
1: Sensor is recognized to be ‘warm’ (containment is not cold)
2: There is minimum of fluid in the containment (release heater)
3: The automatic current correction has reached a limit
4…7: not used
8: The measured current deviates considerably by the desired one
9: The desired or measured current is too low for a measurement
10: The voltage at U- is too high (possibly line resistance too big)
11: Interruption at terminal U+
12: Interruption at terminal U-
13: Interruption at terminal I+
14: Interruption at terminal I-
15: ADC-error when measuring filling level
Multiple interruptions of wires cannot be detected always. There can be additional
interruptions. When I+ and (I- or U-) is broken all four wires are reported to be broken. If
three connections are missing all are marked as broken, too.
Status heater
0: Der heater is ON (Release relay switched on)
1: Der heater is still too warm
2…7: not used
8: Error: Relay didn’t switch on
9: Error: Relay didn’t switch off
10: not used
11: The thermocouple has a short to an external potential
12: The thermocouple has an interruption
13: The hardware interlock is implausible
14: not used
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15: ADC- error when measuring heater temperature
Filling level
A 16 bit word will be sent (EPICS data type WAGO_AI2).
Bit 15: Sign,
Bit 14…3 Value of number (negative in 2-complement),
Bit 2…0 Status of the value.
Status
000: Value is valid
001: Value is not valid (INVALID)
Scaling:
The Value 0 corresponds to a filling level of 0%
The Value 4000 corresponds to a filling level of 100%
Temperature heater (TC)
A 16 bit word will be sent (EPICS data type WAGO_AI2).
Bit 15: Sign,
Bit 14…3 Value of number (negative in 2-complement),
Bit 2…0 Status of the value.
Status
000: Value is valid
001: Value is not valid (INVALID)
Scaling:
The Value 0 corresponds to a temperature of 0 Kelvin.
The Value 3000 corresponds to a temperature of 300 Kelvin.
So, the temperature is sent in steps of 0.1 K.
If the temperature is too low for to be calculated, a replacement value of 30
Kelvin (300) is sent.
Heater output read-back
A 16 bit word will be sent (EPICS data type WAGO_AI2).
Bit 15: Sign,
Bit 14…3 Value of number (negative in 2-complement),
Bit 2…0 Value Status.
Status
000: Value is valid
001: Value is not valid (INVALID)
Scaling:
The Value 0 corresponds to a temperature of 0 Volt.
The Value 0x7ff8 corresponds to a Voltage of 5 V.
Depending on the configuration of the heater analogue control
2 – 2.5 – 4 V correspond to the full heater power.
Command word (output)
Bit 0…1: Mode of operation
00: continuous measurement (current is continuous on)
01: one measurement every 10 seconds
10: one measurement every 30 seconds
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11: one measurement every 60 seconds
Bit 2 Enable-bit of level sensor (since V1.5)
0: Disabled, sensor is off. Heater disabled.
1: Release, normal operation.
Bit 4 Release heater
0: Heater is disabled
1: Heater released
Setpoint filling level (not implemented up to now)
16 Bit number without sign
Bit 15…0: Value
Scaling:
0 corresponds to a filling level of 0
0xffff corresponds to a filling level of 100%
Heater power (external command)
16 Bit number without sign
Bit 15…0: Value
Scaling:
0 corresponds to a heating power of 0
0xffff corresponds to a heating power of 100%
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Settings on the Module There are no settings to be done on modules of the ‘Kryo-I/O-System’, regularly. In case
of the level module some settings can be made. Therefor a DIP-switch with four little
switches can be found on the board. When holding the pulled out module in the left hand
the switch is located at the bottom side. From left to right you find the switches 1 to 4. If
a switch is shifted upwards it is ON and the option connected to this switch is activated.
If the switch points down it is not activated.
Switch 1: No heater.
When this option is
selected the thermocouple
is not read out and the
heater cannot be used. No
heater or TC errors can
occur.
Switch 2: No
thermocouple. This
Option must be used if the
heater doesn’t contain a
thermocouple. In this case
you have to install a
resistor of 100 k
between terminal U- (2)
and AGnd (3). The TC
LED (T) flashes blue if
the simulation is accepted.
The protection of the heater against overheating must be arranged in a different way.
Switch 3 und 4 are not used up to now.
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Technical Data
Current consumption @ 5.2 V 140 mA
Current consumption @ 24 V 380 mA
Maximum resistance of wires (especial I- is critical)
@ 53 mA 28
@ 75 mA 20
Memory usage in the fieldbus data
- data bytes IN* 10
- data bytes OUT** 6
- bytes parameter 4 (3 until V1.3 incl.) * IN: from process to control system **OUT: from control system to process
Measurement repetition rate abt. 1 s
Limitation of the characteristic map by
1. Minimum voltage at the shunt for generating the reference voltage.
2. Maximal voltage, by the input divider.
3. Maximal voltage of the current source is 120 V. R < 120V / I.
4. Maximal current is 100 mA.
Range 0 (100%)…2.5 k
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At higher currents the sensor must have smaller resistances
(length) (see diagram).
Data type INPUT Filling level WAGO_AI2 0…4000 (100%)
Heater temperature WAGO_AI2 in 0.1K
Heating power (read-back) WAGO_AI2 0…0x7ff8 (5V)
Status level sensor UNSIGNED16
Status heater UNSIGNED16
Minimum level (read-back) UNSIGN8 (since V 1.4)
Data type OUTPUT Command (Control Word) UNSIGNED16
Setpoint internal control* UNSIGNED16 0…0xffff (100%)
Heater-output UNSIGNED16 0…0xffff (100%)
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Release Notes
V1.2
- Error diagnostic: U- interruptions under operating current is indicated correctly
now.
- HW-Version 0 or 1 is recognized and the consistency check of the temperature
release is adapted.
- After an error of the level sensor the correction factor of the current source is reset
to 1 again.
- When doing a diagnostic measurement the reference of 5V is used now. Thereby
the ADC is not overdriven anymore and the OVFL-error can be recognized.
- During waiting for a stable value after switching on the current the sensor LED is
flashing green, now. After that a short red flash shows a timeout of waiting.
- New offline diagnostic of level sensor and TC has been installed. It is active when
the field bus is not in data transfer mode.
- When the level sensor is disconnected completely (error U- and I+ recognized) all
lines are reported to be broken now.
- When the TC has sporadic errors (i.e. shorts to AC potentials) or bad contacts the
hardware interlock doesn’t lead to a flattering relay anymore. The recognition is
interrupt controlled now. An error now blocks the heater relay for at least 2
seconds.
V1.3
- Bug in checkProbe() fixed: adcConfig() with correct parameters.
- When recovering from error: when waiting for stabilization first call checkProbe()
with current switched on. This fixes situations of alternating errors which can be
detected only with current on.
- Switch sensor current off when an ADC error is discovered.
- Voltage at U- (versus Shunt-) can be 2.45V now (2.3V before). This limits the
maximum wire resistance of I- wire. Bit 10 of sensor status shows this error.
V1.4
- Minimal filling level for heater release can be configured now in module
parameters.
- Fieldbus-IO: new function for Byte-send (+ Name changed).
- Heater-control: Readback is measured in reference to Vref. Value becomes
invalid, if out of range.
- When servicing an interrupt by an error at TC, the heater relay is switched off
immediately.
V1.5
- Control: Bit 2 must be set to switch on the level sensor.
- When sensor is disabled probe is checked when plugged in.
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V1.6
- The accepted voltage at the TC input may be 12.5 mV now (was 9.1 before).
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Hardware Release Rev. B-1
- F100 is replaced by a resistor of 4.7. Thereby the current source is stable even
under very low load resistance.
- D108 (5V-TVS-diode) is replaced by a Z-diode 4V7. Thereby the ADC is not
overdriven and wrong measurements when doing tests if I- is broken do not apply
anymore.
- R129 changed from 205 to 100. By doing that the gain of the TC-signal is
increased to 805. The heater releasing by hardware interlock is granted at about
210 Kelvin. For the correct consistency checking by the firmware, it checks the
HW-version which is altered from 0 to 1 now (R202 removed).
Hardware Release Rev. B-2
- CC313 (10 nF) is replaced by 100 nF. This avoids an oscillation of the control
loop at low load resistances.