2.6.3.5 - Amplifying Small Signal Voltages [U6 Datasheet]

This section has general information about external signal amplification. The U6 has an outstanding amplifier built-in. Combined with the high resolution capability of the U6, an external amplifier is seldom needed, and in many cases will actually degrade noise and accuracy performance.

For a do-it-yourself solution, the following figure shows an operational amplifier (op-amp) configured as non-inverting:

The gain of this configuration is:

Vout = Vin * (1 + (R2/R1))

100 kΩ is a typical value for R2. Note that if R2=0 (short-circuit) and R1=inf (not installed), a simple buffer with a gain equal to 1 is the result.

There are numerous criteria used to choose an op-amp from the thousands that are available. One of the main criteria is that the op-amp can handle the input and output signal range. Often, a single-supply rail-to-rail input and output (RIRO) is used as it can be powered from Vs and GND and pass signals within the range 0-Vs. The OPA344 from Texas Instruments (ti.com) is good for many 5 volt applications. The max supply rating for the OPA344 is 5.5 volts, so for applications using Vm+/Vm- (±12 volts), the LT1490A from Linear Technologies (linear.com) might be a good option.

The op-amp is used to amplify (and buffer) a signal that is referred to the same ground as the LabJack (single-ended). If instead the signal is differential (i.e. there is a positive and negative signal both of which are different than ground), an instrumentation amplifier (in-amp) should be used. An in-amp converts a differential signal to single-ended, and generally has a simple method to set gain.