# Resistor array and single resistor tolerances

#### Catriona82

Joined Feb 15, 2017
24
Hi guys,

I have a question as I am not sure I am looking at this the correct way....

I have been using a resistor array in a precision instrumentation amplifier which has an abs. tolerance of 0.1% and a ratio tolerance of 0.05%. I can't get these anymore and I can't change the layout of the board so I am thinking of using two single resistors.

I have found one that has a tolerance of 0.05% and I would like to know if I use two of these resistors in place of the network, would the effective tolerance ratio just be the actual tolerance of 0.05% or if there is another calculation I would need to do, to define a ratio tolerance? If so, what would that calculation be?

Joined Mar 10, 2018
3,716
Then ratio tolerance is one R high by .05%, one low by .05%, or vice versa.

Let R1 and R2 represent R's. Let R2/R1 = desired G ideal.

Then ratio = R2 /R1 = (1.0005 * R2) / (0.9995 * R1) = 1.0010 * G so ratio tolerance has increased to .1%

Needless to say at these tolerance levels using an IA with laser trimmed G at time
of manufacture preferred, in light of T and V and aging considerations.

Regards, Dana.