Load Cell Output Signal Amplifier Design

Thread Starter

Czexican1329

Joined Apr 23, 2018
57
E,
Several questions:
1) Why did you set Rg = 365 ohms?
2) If I add a pot in series with Rg, will my value for Rg need to change, i.e. Rg = 365 ohms? And, will adding the pot affect Vout?
3) Do I need to add the 4.7 kohm resistor in parallel to Vout in my circuit design?
4) To decouple my power supply, I need to connect the 100 nF and 47uF capacitors in parallel between V+ and V- (ground), correct?
 

ericgibbs

Joined Jan 29, 2010
9,567
hi,
I chose 365R to give exactly 5Vout for 30mVin.
If I was building that project I would use a 300R 0.01% resistor in series with a 100R cermet 20 turn pot.
The 4k7 is used to help pull down Vout closer to 0V
Always decouple power rails.

BTW: depending upon the Bridge specification, you may need to add some method of 'zeroing' the Vout.
These trim pots are often needed to adjust out the spread in circuit component values.

Remember also you are working with mV signals, so keep the wires short between the bridge and the INA, if necessary screen them.
If you are working in a electrically noisy environment, you may need to R/C filtering on the Bridge lines.

E
 

Thread Starter

Czexican1329

Joined Apr 23, 2018
57
E,
Do you mean a 300 ohm 0.01% resistor in series with a 100 ohm cermet 20 turn pot?
As for decoupling the power rails, my PLC provides a regulated constant 24V, so I believe decoupling is not necessary.

Do you have a suggestions for 'zeroing' Vout?

On the topic of keeping the wires short, that won't be possible due to the size of the project. But the wires of the load cell come in a bare shielding that is supposed to be connected to an isolated ground.

And my PLC will not be working in a noisy environment, so I shouldn't need R/C filtering; but thank you for the consideration.

Lastly, here is my current wiring/circuit diagram:
 

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