CALIBRATION AND MAINTENANCE

UM344-2

6.1.3 RTD/OHM Type Input Calibration

The conversion accuracy of the temperature signal from RTD/Ohm type inputs, as indicated by transmitter output ZERO and FULL SCALE values, depends upon both CURRENT SOURCE and NARROW/WIDE MILLIVOLT calibration (section 6.1.4.2).

The calibration check consists of substituting a resistance decade box for an RTD or Ohm (slidewire potentiometer) type sensor. RTD/Ohm resistances corresponding to ZERO and FULL SCALE values are applied to the transmitter and the 4 mA and 20 mA outputs are checked for accuracy.

The CURRENT SOURCE calibration procedure consists of precisely measuring and storing in the transmitter the value of the RTD/Ohm sensor forcing current.

6.1.3.1 RTD/OHM Calibration Check

1.Connect test equipment to transmitter as shown in Figure 6-1 or 6-2. The decade box is connected in a 3-wire RTD configuration which eliminates the lead wire resistance effect; however, all three test leads should be approximately the same length.

2.Determine zero and full scale resistances for RTD or Ohm type input.

For an RTD type input: consult user supplied RTD resistance/temperature table and record the resistance of the Zero and Full Scale temperatures.

For an Ohm type input: consult user supplied data and record the resistance of the Zero and Full Scale points.

3.Set decade box to resistance corresponding to Zero Scale value.

4.Apply power and read indicated Zero Scale value. Perform either A) or B) and compare the reading to the specifications in step C).

A)Digital Meter installed - read the indicated Zero Scale value on the Meter.

B)Digital Meter not installed - perform the following:

1)From the MXC, execute the FIND XMTR program. (Refer to Section 2 as necessary.)

2)When the MXC finds the transmitter, press the dedicated TRANS VAR'S key on the MXC and read the indicated value.

C)Accuracy specifications:

RTD input

Equal to or less than +/-0.1°C of Zero and Full Scale temperatures.

 

Equal to or less than +/-0.02% of selected span in Deg. C; the higher

 

value will be the accuracy tolerance.

6-6

September 1995

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Siemens UM344-2 user manual 3 RTD/OHM Type Input Calibration, 3.1 RTD/OHM Calibration Check
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UM344-2 specifications

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