Vaisala hmt120 - Testing Analog Outputs; Figure 15 HMT120 Output Current Measurement

5.3 Testing Analog Outputs
The transmitter has a built-in software function for testing analog outputs. To test the outputs:
1. Make sure the transmitter is not in adjustment mode (see Calibration and Adjustment
Overview (page 52)).
2. Press the + adjustment button (see Figure 11 (page 21)).
This sets the output current level to the high point of the analog output range (20mA
nominal). The output stays at this level for about 30 seconds after the + adjustment
button has been pressed.
3. Press the - adjustment button. This sets the output current level to the low point of the
analog output range (4mA nominal). The output stays at this level for about 30 seconds
after the - adjustment button has been pressed.
HMT120 analog output current can be measured without removing the wires from
the screw terminals by using a low-impedance multimeter between the
associated + terminal and test point (CH1 or CH2) on the component board (see
Figure 15 (page 50)).
1 SHLD
2 CH1-
3 CH1+
4 CH2-
5 CH2+
mA
mA
+ -
+ -
CH1 TEST
CH2 TEST
Figure 15 HMT120 Output Current Measurement
If your transmitter has the optional display, the following texts are shown on the
display the during analog output test:
• Analog output test high: analog output set to upper limit (20 mA)
• Analog output test low: analog output set to low limit (4 mA)
HMT120 User Guide M211244EN-C
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