Before You buy new Chips ..........,
Connect "REF" to a 1K-1K-Resistor-Voltage-Divider, ( providing 1/2 of the Supply Voltage ).
I was surprised to see someone say that it should be connected to Ground,
and maybe that's standard practice, but I've never seen it done.
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I was surprised to see someone say that it should be connected to Ground

If using a single supply and do not need negative readings connecting REF to ground is normal.

 

hi LowQ,
Ideally it should be a Low impedance Vref source voltage, but a quick and simple [ depending on the project] is a IN914 to ground, driven via resistor to +v, raising approx +0.7V

With a single supply, a Vref ground will give an approx +0.3v offset with a zero mV input.

Ground is OK with a dual power supply

E

 

The circuit the TS posted is virtually the same as listed on the data sheet in this diagram.
See note 1.

 

I'm just not so sure about those Chips having "Rail-to-Rail" Inputs and Outputs.
You never know what you'll get from China.
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You never know what you'll get from China.

Exactly. I think we have established the chips are defective.

 

Before You buy new Chips ..........,
Connect "REF" to a 1K-1K-Resistor-Voltage-Divider, ( providing 1/2 of the Supply Voltage ).
I was surprised to see someone say that it should be connected to Ground,
and maybe that's standard practice, but I've never seen it done.
.
.
.

Just tried that

REF to GND = 1.777v
Output to REF = 2.67v
Signal = 0.00mv (shorted pin2 and pin3)
Power supply = 5v

unfortunately still does not work

 

I'm just not so sure about those Chips having "Rail-to-Rail" Inputs and Outputs.
You never know what you'll get from China.
.
.
.

Exactly. I think we have established the chips are defective.

Well, maybe I will buy my next chip from mouser or digikey in Hong Kong

Huge thanks for helping me <3

 

the black wire is ground, which should be connected to the negative terminal of the power source

and And AND -- to the V- and reference pins of the INA122, pins 4 and 5.

Still have not seen *your* schematic with all input and output connections.

ak

 

Connect "REF" to a 1K-1K-Resistor-Voltage-Divider, ( providing 1/2 of the Supply Voltage ).
I was surprised to see someone say that it should be connected to Ground,
and maybe that's standard practice, but I've never seen it done.

The chip's input common mode voltage range includes GND. Also, there are single-rail circuits in the app section of the datasheet. Pages 8 and 9 in the October, 1997 version.

ak

 

Hi psam,
The problem with a single supply and Vref at 0V you get this result on the Vout.

ie: not 0v to 25mV , but with a +Offset voltage, to which the 0v to 25mV will be added.

What are you doing with the 25mV Vout signal.?
E

 

Hi psam,
The problem with a single supply and Vref at 0V you get this result on the Vout.

ie: not 0v to 25mV , but with a +Offset voltage, to which the 0v to 25mV will be added.

What are you doing with the 25mV Vout signal.?
E
View attachment 254857

25mV is for testing purpose since I don't have to connect Rg. My idea is: The more components I connect to a developing circuit, the more components to be diagnosis and debug.
After getting a working IC/circuit, I will put a VR across Rg and set it to 201ohm so that I can have a gain of 1000V/V and have a 5v output

and the current problem is:
whatever the output should be, the output now is always 4.4V when supply = 5V and Vref=0v

 

and the current problem is:
whatever the output should be, the output now is always 4.4V when supply = 5V and Vref=0v

hi,
I think we all agree the INA122's you have are defective.

I would not agree with your logic about partly building this INA without the Rg.
For Testing place a 200R across Rg, this will be a more realistic Vout for testing the following circuits, it will also highlight any other possible problems in part of the circuit.

E


Update:
Note the non-linearity at the low levels of output.

 

hi,
I think we all agree the INA122's you have are defective.

I would not agree with your logic about partly building this INA without the Rg.
For Testing place a 200R across Rg, this will be a more realistic Vout for testing the following circuits, it will also highlight any other possible problems in part of the circuit.

E

oh great! I will place a 200ohm resistor across Rg.

Update:
Note the non-linearity at the low levels of output.

Noted! thanks! <3

 

With Rg open, the circuit should have a gain of 5. I don't see that in #51.

the current problem is:
whatever the output should be, the output now is always 4.4V when supply = 5V and Vref=0v

My read of post #27 is that R2 - R5 in post #51 are not needed if the cell Vcc and GND and the circuit Vcc and GND are the same and connected. Do you have any other opamps available that are known to be good?

ak

 

hi analog
R2 - R5 in post #51 are the internal Load Cell elements.
E

V2 is a superimposed 5mV test signal

 

I'm surprised at the low values, but ok.

ak

 

Hi, sorry to revive this post, were you able to fix the problem? Im having the same problem, same fixed output no matter what... Thinking on buying new amplifiers but in the meantime im trying to fix it

 

Hi, sorry to revive this post, were you able to fix the problem? Im having the same problem, same fixed output no matter what... Thinking on buying new amplifiers but in the meantime im trying to fix it

I gave up on using INA122p and I used three rail-to-rail op amps instead