Hello everyone,

We want to amplify voltage comes from load cell & thermocouple with AD620 A (SOIC) chip. We designed a circuit as two channel as in the attachment and wired. But the output voltage is not increase as discused on datasheet.

Could you please look the circuit and suggest improvements?
Thanks with kind regards.

 

There is an example thermocouple circuit on page 17 of the AD620 datasheet. Does your circuit correspond to that?
Post your circuit diagram..

 

hi dogan,
Your pcb circuit layout does not make any sense.?
Please post a circuit schematic.
E

 

Thanks for your quick replies,

I am sending the circuit schematic at the attachment. I want to measure from PT100 and another type of thermocouple BT01 (bayonet type thermocouple). Additionally, I am connecting loadcell's signal +/- to pins 2/3 and power is connecting from another power supply.

I will try drc_567 suggesstion asap.
thanks with kind regards.
d

 

You make reference to a "thermocouple:;

"a thermoelectric device for measuring temperature, consisting of two wires of different metals connected at two points, a voltage being developed between the two junctions in proportion to the temperature difference".

A thermocouple would need a CJC (Cold Junction Compensation) reference. Then you also make reference to a PT100 which is not a thermocouple:

"A platinum resistance thermometer with a resistance of 100 Ω at 0°C that is consistent in the IEC and JIS standards. The platinum resistance thermometer that is unique to the JIS standard is called "JPt100."

The illustration on page 17 of the AD620 Instrumentation Amplifier Data Sheet Figure 47. Ground Returns for Bias Currents with Thermocouple Inputs provides a rough but CJC still needs considered if an actual thermocouple is used. A PRT is a different type of temperature sensor than a thermocouple. What exactly do you have and what exactly are you trying to do. That said what does or does not work as expected?

Ron

 

Is this a school/college project?

 

The schematic shows no basic understanding of how to use an OpAmp....

 

The schematic shows no basic understanding of how to use an OpAmp....

That's because it's not an opamp, it's an instrumentation amp, but he shows no understanding of that either.

 

You need a ground connection for the power supply, a connection referenced to ground for the REF input, as well as a bias path to ground for the inputs.

It also needs a dual power supply.

All circuits require a ground reference and yours has none.
Did you not learn about grounding and ground paths for circuits in your training?

 

.........I want to measure from PT100 and another type of thermocouple BT01

A PT100 is a resistive temperature sensor that changes resistance with temperature.
It requires a bias voltage to measure the resistance.

A thermocouple does generate it's own voltage and thus requires no external bias.