Question: I have a 4-20mA sensor that measures the water level. It is connected correctly to the TRMC-5. If I measure the current with a multimeter, I get 5.2mA, but if I measure with the TRMC, I get 4mA. What is this coming from?



Answer: To save energy, the TRMC switches off the 4-20mA probes and only turns them on for the measurement. If the measurement is taken immediately after switching on the probe, the probe may not be ready. It usually needs to be given time (typically 2-5 seconds, but see manufacturer's doc) for it to make a measurement and output a correct signal. During "manual" tests, with a multimeter, the probe is usually switched on several seconds before the values are looked at.



To solve this problem, add a WAIT statement to the acquisition sequence after the PROBES_POWER.




<PROBES_POWER state="8"/>
<WAIT timeout="3"/>
<ACQ header="178" port="7" channel="2" timeout="3"/>
<ACQ header="161" port="7" channel="3" timeout="3"/><PROBES_POWER state="0"/>