4-20mA output Single-Channel Terminal Board and TC-08

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4-20mA output Single-Channel Terminal Board and TC-08

Post by tost » Mon Oct 01, 2018 3:01 pm

I am new to data logging with little knowledge of voltage type signals and connections.

I have an instrument (gas analyser) with 4 paired cables that sends an output of 4-20mA signals. I have a Pico TC-08 data logger and I just recently purchased 4 Single-Channel Terminal Boards to do this, but I am not sure if i am doing this correctly or i need an intermediate step to generate mV readings.

What I have done so far?
Followed the step by step guide to "Measuring voltages and currents"

1.Connected the negative side of the circuit to the COM terminal.
2.Connected the positive side of the circuit to the “5 V” for a 4-20 mA loop signal
3.Set the switch for the 4-20 mA loop signal to “ON”
4.Plugged the terminal board into the USB TC-08.
5.Connected the USB TC-08 to the computer and completed PicoLog setup for mV

I am getting readings that do not match the readings from the analyser. I know I have to apply scaling factors but I am not sure if I am generating "mV" signals correctly. Do I need to add a resistor somewhere for this mA loop signals or together using the wrong set-up with these single channels?

I do have a ADC24 but the guide appears more complicated, so I would appreciate a step-by-step guide if possible with images.

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Re: 4-20mA output Single-Channel Terminal Board and TC-08

Post by Martyn » Tue Oct 02, 2018 5:23 am

That looks correct.

How is the Gas Analyzer powered ? and where is it's ground connection in relation to the PC and TC08 ?
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Re: 4-20mA output Single-Channel Terminal Board and TC-08

Post by tost » Tue Oct 02, 2018 3:08 pm

I have connected the analyser to the mains (240VAC). From the manual "Current output sink is connected to chassis (nominally ground)" |Regarding connections to TC-08 and PC, the analyser uses an analog cable and I have followed the instruction in the image attached.
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Re: 4-20mA output Single-Channel Terminal Board and TC-08

Post by tost » Tue Oct 02, 2018 3:39 pm

The analyser is connected to the mains (240VAC). From the manual, the current output sink is connected to chassis (nominally ground). I dont know if that answers the second question. the connection to the TC-08 is an "analogue output pin connection-a circular "DIN‟ connector ". It has 8 pins and cables. each pair correspond to the four gases that the instrument reads. I have connected each pair to 1 single channel terminal board.

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Re: 4-20mA output Single-Channel Terminal Board and TC-08

Post by Martyn » Wed Oct 03, 2018 7:19 am

Cam you post a picolog data file so that we can look at the setup and readings, it all looks OK but may just need the correct scaling applied according to the voltage.

We would also need to know the scaling for the sensors from the datasheet.
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