7
3.0
CALIBRATING THE TRANSMITTER (Continued)
To calibrate the transmitter, follow these steps (refer to Figure 3-1):
1.
Locate the model number in Table 3-1 or 3-2 and set the millivolt source to the
LO-IN value.
2.
Adjust the Zero potentiometer until the milliammeter reads 4.00 mA.
3.
Set the millivolt source to the HI-IN value (in your appropriate table) and read
the output current on the milliammeter. This current level is designated Initial
Top Current (ITC), normally not equal to 20.00mA.
4.
Calculate the Corrected Top Current (CTC) using the following equation (gener-
ally this will not equal 20.00mA):
CTC = 16 x ITC / (ITC - 4 mA)
5.
Adjust the Span potentiometer to obtain the CTC on the milliammeter.
6.
Now re-adjust the Zero potentiometer so that the milliammeter reads 20.00 mA.
7.
Set the millivolt source to LO-IN millivolts. If the output current is not
4.00 mA, repeat steps 2 through 7.
6.
When calibration is complete, remove the transmitter from the setup.
An thermocouple calibrator may be used in place of the millivolt source - refer to
Figure 3-2.
Figure 3-2. Calibration using a Thermocouple Simulator
1
2
3
4
5
ZS
DMM
(4–20 mA)
MONITOR
(–)
(+)
(–)
(+)
250 Ohms
INPUT
THERMOCOUPLE
WIRE
SPAN
ZERO
THERMOCOUPLE
CALIBRATOR
DC SUPPLY
24 VDC
Summary of Contents for TX90A Series
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