Repected sir,

We have use the temperature + Humidity transmitter (two wire loop transmitter) which gives 4-20 mA output, distance between transmitter and controller approximately about 150mt, and wire used for that transmission is screen shielded cable, SMPS used for excitation voltage makes two wire loop (24v DC, 2 Amp). Now our problem is we can't get the proper signal at controller end.

please suggest the solution which gives the output continuously and accurate. please do the needful.

regards,
tejas

 

When you use a 2 wire transmitter the following should be ensured.
1.The 24 volts is capable of taking the load.
2.The resistance of your wire is the minimum.

I have also experienced the same problem when I use a PT100 TO MA convertor at the field.There is quite a substantial difference in the measured temperature and the ma at the controller end.I think it would be prudent to keep the cable distance to about 10- 25 m at the most,or try to use a sensor which can send the temp/humidity data via rs 485.

bye
Santhosh Jayarajan
Malaysia

 

4-20 mA signal should be able to run 1-2 km depending on the wire used

What is the problem you are facing? Current too high? Too low? Unstable?

Voltage at power supply is 24 VDC. What is the drop across the transmitter output? Across the controller input? And along the wires? Check these at both 4 mA and 20 mA. Check the current in the loop as well.

Jonas Berge
SMAR
===========
[email protected]
www.smar.com
Learn fieldbus and Ethernet at your own pace: www.isa.org/fieldbuses
Learn OPC and automation software at your own pace: www.isa.org/autosoftware