-VE VOLTAGE OUT IN BRIDGE PRESSURE SENSOR

Thread Starter

AJIN NADH

Joined Dec 18, 2014
84
Hi,
I am using 2smpp pressure sensor,and the output is showing from-3.3 to 4.0mv , this output voltage is amplified using an instrumentation amplifier ad623 in single supply. The problem is ad623 is not amplifying the -ve voltage , But I need -ve value's to be amplified, Can any body suggest solution...?
 

bertus

Joined Apr 5, 2008
20,059
Hello,

When an amplifier is powered with a single supply, you can not amplify the negative voltages.
For that you will need to use a dual powersupply.

Bertus
 

Thread Starter

AJIN NADH

Joined Dec 18, 2014
84
Hello,

When an amplifier is powered with a single supply, you can not amplify the negative voltages.
For that you will need to use a dual powersupply.

Bertus
Is there any other way ...without using dual supply, Can i change this -ve sensor out to +ve...?
 

pwdixon

Joined Oct 11, 2012
488
Assuming you meant -3.3mV to +4mV looking at the datasheet for a 2smpp the offset is -2.5mV+/-4mV meaning that you are trying to measure a very low pressure and not much of the overall range of this sensor.

Not sure if this will work but the datasheet for the amplifier says it will allow an input that is negative and there is a Vref pin to allow some control over output offset.

see datasheet:

REFERENCE 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 because it
can be used to provide a virtual ground voltage. The voltage on
the reference terminal can be varied from −VS to +VS.

so perhaps using a voltage on Vref you could shift the output so that it is all positive, only a maybe and would need some test/verification.

Of course if this is some kind of production item you might have to worry about the +/-4mV variability of the sensors.
 

Thread Starter

AJIN NADH

Joined Dec 18, 2014
84
Thanks for your valuable support,
We did it by giving a reference voltage, by adjusting the reference voltage using a 100k pot.
 

ericgibbs

Joined Jan 29, 2010
8,744
hi,
Using a 100K pot to set the Vref is a bad idea, the Vref source MUST be a low impedance source if you want accurate readings.
Ajin, do you have a circuit diagram to post.?

E

EDIT:

This clip from the d/s for the AD623 shows how to connect a low CMV sensor.
The 2Vref in the example, must have a low impedance source, ideally a OPA output
 

Attachments

Last edited:
Top