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Problem with the differential voltage mode

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Problem with the differential voltage mode

Postby Guest » Tue Apr 15, 2008 10:04 am


I'm using the pico pt-104 in order to mesure a temperature.
I have a type T thermocouple which is connected to an amplification circuit.
This circuit is made of a RC low pass filter, and then a AD595CQ which gives a 10 mV/°C output.
This output is connected to the pt104.
This is not me who have made these connections, and I have a few question about that.

First, V+(pin 2) is connected to the positive voltage of the AD595, V-(pin3) to the negative, and V- is connected to ground(pin4) via a 100kohm resistor. Is this the good way?

I use the software given with the pt104 to watch the voltage. This voltage seems quite correct, but when I unplug the pins, I still have the same voltage. Is it normal? Why don't I have then 0V (or nearly?)

The pt104 is also used to mesure a thermal flux via a thermal flux sensor. In this montage, there is no resistor between V- and ground, theses 2 pins are just connected. Why this difference?

Thanks a lot for the answers, and sorry for my english ;)


Postby picojohn » Fri Apr 18, 2008 3:00 pm

Hello Mille,

From the description that you have given, your voltage source is single-ended and connected incorrectly to the PT-104. Please refer to the connection instructions in section 2.3 of the user manual (http://www.picotech.com/document/pdf/pt104.pdf).

The 0v of your source should be connected to the PT-104 GND and the +ve to the PT-104 +ve input. In PicoLog, configure the PT-104 for single-ended voltage 0-2.5v.

It is not clear why you hace the 100k resistor included in your setup?

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