Dear Researchers,
I'm working on a bridge circuit that is connected to an instrumentation amplifier AD623. The differential inputs to the amplifier from the bridge (-IN and +IN) reads 2.45V each respectively implying the balanced condition of the bridge. I used a resistor gain of 218 Ohms . So am expecting the output to be amplified 458 times the differential input. However, the output always reads 3.83V irrespective of the resistor gain I use. I used two different power sources to power my bridge and amplifier (say +5,-5V respectively). Why is this problem occuring? I clearly see the problem occurs only after amplification. Before amplification, the tester reads almost zero voltage. In some articles, I see people are using two capacitors across the positive voltage source of amplifier (Please see attached figure). Any help would be much appreciated. Thank you
the amplification gain is G = 1 + (100 k/RG) = 459,715596
there are many types of resistor according to the manufacturing tolerance
if you use a resistor with 10% tolerance you may have 10% tolerance in gain
try to choose a good resistors witch have a tolerance of 1% or 0.1% .
the tester or voltmeter that you use has an internal impedance witch change according to the caliber, it would be generally near 100kΩ for a digital voltmeter.
you should first use a low Gain value in example G = 1 then you could rise it.
for the output you should have a load of 10 kΩ
the maximum output = (+VS) −1.5V generally.
if you need higher output voltage use another amplifier that could support higher voltage.
for good results input frequency must be less than 100 hz (read datasheet).
you didn't give us any information about the input.
if you need only the steady state value put small ceramic capacitance on the input between in+ and in-, example 1nf.
Connect the reference pin to the ground ( 0V).
Good Luck
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