Rosemount TankRadar Rex DAU 2100, Service Manual

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4-57
Rosemount Tank Radar Rex
Chapter 4 Service
Service Manual
308012En, Ed.2
May 2013
4.3.3 Exchanging the External Reference Resistor
The external reference resistor must be changed if a different
temperature measurement range will be used, see 4.3.1. Also, if the local
display shows a reference resistor calibration error, it may be necessary
to replace it. The reference resistor is connected to channel 15 of the
multiplexer.
The reference resistance values corresponding to different temperature
ranges and sensors are given in the table below.
Figure 4-28 illustrates how to connect the external reference resistor to
the X21 terminal.
Figure 4-28. Connection of reference resistor
Automatic test of reference resistors
The internal reference resistor is placed on the Motherboard. The ratio
between the high and low temperature references is calculated as a test
of the reference resistors. This value is compared with a value given for
the current temperature range. The ratio is allowed to deviate a certain
amount from the nominal value. The tolerated deviation can be viewed in
holding registers 307-310.
Resistance (

) Temperature range (°C)
138.50 -50 - +125
175.84 -50 - 300
24.90 -200 - +150
The X21 terminal
Connect
temperature
sensors
Connect
Reference
Resistor
to terminals
43, 44 and 45.