How to obtain output from AD623

[mesamune80]

Hi all,

Anyone knows the way to get the output from the device AD623 ?I go through the data sheet and it said i need to tie the REF pin to the Gnd,but i could not get any voltage changes ,when i followed this way .I supposed to get a change in voltage as the input changes?
anyone know the way?
Thanks.

 

[ericgibbs]

hi,
Can you post a drawing showing how the AD623 is connected?

 

[mesamune80]

My AD623 is connected as below:

**broken link removed**

i am not sure where the REF Pin should be connected,i try to ground it before but it couldn't work.
Thanks.

 

[ericgibbs]

hi,
Where are the +V1 and +V2 pins connected to?

What is the output Voltage?

For a test, replace the 100K pot with a 2K0, this will give a Gain of approx *50.

Connect the REF pin to 0V.

REF TERMINAL
The reference terminal potential defines the zero output voltage and is especially useful when the load does not share a precise
ground with the rest of the system.
It provides a direct means of injecting a precise offset to the output.
The reference terminal is also useful when bipolar signals are being amplified as it can be used to provide a virtual ground voltage.
The voltage on thereference terminal can be varied from –VS to +VS.

 

[mesamune80]

For your info the +V1 and +V2 pin is connected to a force sensor
the data sheet for the forsensor can be obtained below:
https://www.electro-tech-online.com/custompdfs/2007/05/0900766b8002e121.pdf
The output voltage will change according tothe change in force that exerted.
because the output for the sensor is in the range or mV ,what i desired is the output can be amplified by AD623 form mV to V which is 1000 gain,as i use the 100R instaed of 100k for R7.
So in order for me to get the output reading can i connect the REF pin to 5V?
Thanks.

 

[ericgibbs]

hi,
I understand that you require *1000 for the final circuit when using the force sensor, ie: 100K0 resistor.
I suggest a lower Rg value in order to check the AD623.

The sensor is a bridge configuration, how are you powering the sensor? What are the voltages?

The REF pin is used to inject a correction voltage into the AD623 that will cancel any 'offset in the output' caused by different power/ground voltages at the inputs of the AD623.

As the datasheet states, the REF voltage can be +/-Vsupply.
You have not answered my question regarding the output voltage?
If you want to use the REF pin, I would suggest that you connect a pot [100k], between +5V and -5V, with the wiper connected to REF via a 10K0 resistor.
By adjusting the REF pot, you should be able to set the AD623 output to zero.
I suspect that at the moment its at 0V or +5V without the pot.[ with Rg=100K0, a Gain of 1000]

EDIT: look at Fig 49 of the datasheet, for how to use the REF pin voltage.
If you give me answers I maybe able to help.

 

[mesamune80]

i am not sure what is the output voltage yet because it depends on the force that exerted.moreover the output voltage will later go to a windows detector circuit.now i need to check the output voltage from AD623 after the amplification.what is the typical value?
for the Rg i am using pot to (act as variable resistor)to obtained the resistance value.which is ~100R
the sensor i powering with +12Vdc.
and there will be some voltage value(mV) if the force sensor is activated.and some force are exerted on the panel.
One question here what is the best way for me to get +5V and -5V supply?
Any IC would do the job?

 

[ericgibbs]

hi,

You are powering the sensor bridge with +12V, so the mid point of the bridge outputs is at +6V.
The AD623 diagram shows its powered with +5V, so look at the datasheet for the Common Mode input voltage
will it tolerate when powered from +5V????

Can you power the sensor from +5V as a test??? [CMV will +2.5V]

EDIT:
A quick look at the sensor data, shows no minimum excitation voltage, so it should work at +5Vx.
I realise that the sensitivity will be reduced to 50%, but it will give you the basis of a working system.
Another important point, is the bridge is ratiometric.
For testing connect a 10K0 from the AD623 output to 0V.

 

[ericgibbs]

hi,
The AD623 datasheet shows that it can operate from a single supply of +12V. You double check this!.

If the sensor specification is +12V, why dont you power the AD623 with +12V??

This will solve the Common Mode input voltage problem also connect a 10K0 from the output to 0V. At this time ground the REF pin to 0V.

This will give you working system, if you then find that you have an output voltage offset, when the sensor is at 'balance' then apply a offset correction voltage to the REF pin to cancel the output offset.
The offset voltage could be either +/-so you may have to connect a -Vref to the REF pin. BUT for now just connect REF to 0V.

Let me know what you find.

EDIT:

 

[mesamune80]

Ok.ya the sensitivity will be lowered if use lower voltage to power the sensor.
i'll try out +5V to power the sensor and connet a 10kR to ground.

 

[mesamune80]

Ya,the AD623 can be power with +12V (maximum),i'll try to power it with +12V this can keep the sensitivity of the sensor and solve the common mode input problem.So my new circuit configuration would be like this:
**broken link removed**
Hope this will do the job.

 

[ericgibbs]

hi,
Thats the way I would try it.

Good Luck.

 

[mesamune80]

Just tested the circuit ! ! !
i put a load(~10K)actually is [20k in parallel] between pin 6(Output pin of AD623) and ground this time i use +12V to power up both the sensor and AD623 and common out the ground.this time i test without the wiper circuit connected to the AD623's REF pin i straight away ground it.That's why i got a offset voltage about 2.0V from the output.Next time i'll test it by using the wiper circuit so that my output is a nice zero V!!!! ^_^