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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 ● sales@kelleramerica.com

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

T emper at ur e

T emper at ur e

  T a  r g e

  t   p  r e s

 s  u  r e 

  i  n  b

  T a  r g e

  t   p  r e s

 s  u  r e 

  i  n  b

   E  r  r  o

  r   i  n  m   b  a  r

   E

  r  r  o  r   i  n  m   b  a  r