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Conversion Devices

These Virtual Devices change one type of unit to another.

RTD to Temperature Converter

The RTD to temperature conversion Device converts resistances from RTD sensors into temperatures. This Device supports both PT100 and PT1000 sensors, and it has programmable R0 (resistance at 0 degrees C) and Callendar-Van Dusen coefficients to support most any other type of RTD sensor. It also has a programmable number of inputs and outputs, so one Device can handle many RTD sensors. It works well when its inputs are Virtually Wired to the outputs of a ProtoVoltaics RTD Shield Device.

Temperature values are computed by solving the Callendar-Van Dusen quadratic equation when temperature values are greater than or equal to 0 degrees C; for colder temperatures, temperature values are computed by solving the Callendar-Van Dusen equation using Newton's method.

Terminal Description

The RTD to temperature conversion Device has user defined inputs and outputs. For each input defined, there must be a corresponding output. Each input takes a resistance value (in ohms) and converts it to a temperature (in either Fahrenheit or Celsius) based on the Device's Callendar-Van Dusen coefficients and its R0 value.

Configuring the RTD to Temperature Converter

By default, the RTD to temperature conversion Device is configured for a PT100 sensor with an alpha of 0.003850. The Callendar-Van Dusen coefficients are pre-set to: A=3.90830e-3, B=-5.77500e-7, and C=-4.18301e-12. These coefficients are programmable. When entering a coefficient, enter it in its pure decimal form (no exponents allowed). The output temperature can be either in degrees Celsius or Fahrenheit.

The RTD to temperature conversion Device has the following configuration parameters:

  • inputs : a string of comma separated input names. These inputs expect input values in ohms.
  • outputs : a string of comma separated output names. For each input, there needs to be an output. Output values can be in either degrees Celsius or Fahrenheit.
  • temperature_units : determines whether the Device outputs in Celsius or Fahrenheit. Expects the string "C" or "F".
  • r0 : - the resistance of the RTD when it is at 0 degrees C (100 for a PT100).
  • a : the Callendar-Van Dusen A coefficient
  • b : the Callendar-Van Dusen B coefficient
  • c : the Callendar-Van Dusen C coefficient

Configuration Example

The following parameters create an RTD to temperature conversion Device for 3 separate PT1000 sensors. Temperatures are output in Fahrenheit. The Device has input terminals named in1, in2, and in3, and output terminals named out1, out2, and out3. The Device uses the default Callendar-Van Dusen coefficients and has the ID "rtd2temp".

id: "rtd2temp"
inputs: "in1, in2, in3"
outputs: "out1, out2, out3"
temperature_units: "F"
r0: 1000

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Page last updated: Tue Jul 14 22:58:56 2015 (UTC)