Test and Measurement Forum

We currently use TC-08s for temperature measuring. To measure the state of the power supply to the product that we are testing, we attached a thermocouple to the supply cord and we can then, through the temperature generated in the supplly cord, tell roughly when the supply turns on and off. We would like to have a more accurate method of doing this.

Our initial thinking is to break into the supply and reduce the voltage to a small DC voltage and using the single channel terminal board, we should be able to tell when the supply is on and off.

Is it possible to measure temperature and voltage at the same time on the TC-08?
Does Pico supply anything that we can use to reduce the voltage down to the appropiate voltage?
Is there another way to do this?

Thanks

Michael

There is no problem in measuring voltage and temperature at the same time (but of course on different channels).

Input is limited to app. 70 mV in voltage mode, so use a simple resistor based voltage divider to reduce your supply voltage to an appropriate voltage less than 70 mV.

Then use a two pair table lookup either direct on input channel calculation or create a calculated parameter.
If your supply is e.g 24.00 V DC and the input channel read e.g. 65,7 mV the table should look like:

raw scaled
0 0
65.7 24000

Scaled parameter = mV

or format Units to Volt:
raw scaled
0 0
65.7 24.0

Use neutral (white) copper-copper mini plugs.

Thanks for your reply Ole.

Michael

Hi There,

Thankyou for your posts with regard to measuring voltage on the TC-08.

We do supply a single channel terminal board that has been designed specifically for use with the TC-08.

Introduction

The USB TC-08 Single-Channel Terminal Board is an accessory for the Pico Technology USB TC-08 8-Channel Thermocouple Data Logger. The screw terminals allow wires to be attached to the data logger without soldering and enable the USB TC-08 to measure voltages from 0 to + 5 V or 4-20 mA loop currents. The terminal board is designed for use with the USB TC-08 and is not guaranteed to work with other thermocouple data loggers.

Inputs and switch
Name Function
4-20/5V Input for the positive side of a 4-20 mA loop or 0 to
5 V signal.
500mV Input for the positive side of a 0 to 500 mV signal.
50mV Input for the positive side of a 0 to 50 mV signal.
COM Input for the negative side of any voltage or current
signal.
4-20 mA Set switch to “ON” for a 4-20 mA loop signal.
Set switch to “OFF” for all voltage signals.

Measuring voltages and currents
1) Connect the negative side of your circuit to the COM terminal.
2) Connect the positive side of your circuit to the “5 V”, “500 mV” or “50 mV”
terminal depending on the voltage range of the signal. For a 4-20 mA loop
signal, use the “5 V” input.
3) For a 4-20 mA loop signal, set the switch to “ON”. For a voltage signal, set the
switch to “OFF”.
4) Plug the terminal board into the USB TC-08.
5) Connect the USB TC-08 to the computer using the USB cable supplied with the logger.
6) Run PicoLog on the computer.
7) Go to File -> New Settings.
Set the converter type to USB TC-08.
9) Edit one of the USB TC-08 channels and set the “Thermocouple” control to“mV”.
10) PicoLog will display the voltage or current applied to the terminal board in the monitor window.

http://www.picotech.com/thermocouple.html

The voltage displayed in PicoLog corresponds to the input voltage as follows:
Input range PicoLog voltage
0 – 5 V 0 – 50 mV
0 – 500 mV 0 – 50 mV
0 – 50 mV 0 – 50 mV
4 – 20 mA 9.6 – 48 mV

If you require further assistance on this please do not hesitate to contact me via support@picotech.com

Hi

I have the single channel terminal board with my Pico and have not used it yet as I want to also measure pressure using a transducer that is rated 4-20mA.

However, the reason I have not used it yet is that the supply I want to use for the transducer to work is a 24Vdc power supply to feed the positive side of the transducer. I would then connect the negative connection to the single channel board and then the common on the board to the 0V on the power supply.

My question is, would this work or is the 24Vdc power supply too large and should I be looking at a lower power transducer with a lower voltage rating.

I'm worried about destroying my pico by using a 24Vdc power supply to feed the transducer and that is why I have not tried it yet.

Could you let me know if this is ok please anyone

Hi Michael,
The TC-08 inputs are safe from damage up to +/-30V but will not take correct measurements if the Common Mode voltage applied is greater than about +/-5V on any channel or the differential voltage is greater than 70mV. The "Single Channel Terminal Board", when set to 4-20mA input, puts a resistive load from the input to ground of 240 ohms so the maximum current output of your sensor (20mA) will only develop a maximum of 4.8V across this resistor. There is then a 101:1 attenuator which reduces this voltage down to 47.5mV.
You are quite safe to use your 24V power supply.
Regards,
PeterF.