Digital Transmitter Overview
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Transcript of Digital Transmitter Overview
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8/13/2019 Digital Transmitter Overview
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Digital Pressure Transmitters
Preciseline / Acculevel: Fast, digitally compensated pressure transmitters with analog output
The sensor signal is measured 400 times per second with a highly precise A/D converter(16bit). After each measurement, the exact pressure value is calculated, thereby eliminatingthe linearity and temperature errors. The analog output signal is updated via the D/A converter.
This technology allows highly precise and fast pressure measurements, even over broadtemperature ranges.
Analog Output
The analog output is scalable and is offered in the following formats:
• Voltage output: 0 – 10 V
• Current output (2-wire): 4 – 20 mA
The outputs are protected against reverse polarity and short-circuit.
Digital Interface
In addition to the analog signal output, these pressure transmitters offer a digital, bus-capableinterface, offering the following features:
• Read-out of the pressure and temperature values
• User adjustment of zero and gain
• Scaling of the analog output to other pressure ranges or units
• Configuration settings
• Read-out of information, such as serial number, compensated pressure and temperature ranges
• Two wire RS485 half-duplex with 9,600 baud or 115,200 baud.
Digital Compensation Technology
Non-linearities and temperature dependencies of the pressure sensor are eliminated to a largeextent with a mathematical model of the sensor. In production, each pressure transmitter ismeasured over the entire temperature and pressure range. These measurment values are thebasis for the mathematical model.
In operation, the following formula calculates the exact, “error-corrected” pressure value:
p: Calculated pressure value
temperature: Measured temperature at the sensor
pressure: Measured pressure sensor signal
coeff: Coefficients
n, m: Order of the polynomials. Value range: 1 – 3
p = ∑ (∑ coeff i,k * temperature k ) * pressure n m
i = 0 k = 0
Preciseline(Shown larger than actual size)
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Keller America, Inc.
813 Diligence Drive ● Suite 120 ● Newport News VA 23606 ● Toll Free: (877) 2-KELLER ● Local: (757) 596-6680 ● Fax: (757) 596-6659
www.kelleramerica.com ● [email protected]
Copyright © 2004 Keller America, Inc. All Rights Reserved
Preciseline / AcculevelThis compensation technology typically reduces the error band to 0.05 %FS over the entire pressureand temperature range, which is an improvement by a factor of 20 to 50 (see graphics below).
Shown below are error “maps” of conventional and digitally-compensated transmitters, pressurerange 0 – 10 bar, temperature range -10 – 80ºC.
Conventional Transmitter
Digitally compensated Transmitter
Acculevel
11.01.0
(Shown larger than actual size)
1 0 8
6 4
2 0
1 0 8
6 4
2 0
-10º C 10 25 50 80º C
-10º C 10 25 50 80º C
100
50
0
-50
-100
100
50
0
-50
-100
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