miniLAB 1008 User's Guide
Functional
Details
Differential configuration
When all of the analog input channels are configured for differential input mode, four
analog channels are available. In differential mode, the input signal is measured with
respect to the low input.
The input signal is delivered through three wires:
The wire carrying the signal to be measured connects to CH<0, 2, 4, 6> IN. In
differential mode, the even numbered channels are considered HI inputs. Hence,
CH0 IN, CH2 IN, CH4 IN and CH6 IN are considered HI input channels.
The wire carrying the reference signal connects to CH<1, 3, 5, 7> IN. In differential
mode the odd numbered channels are considered the LO input. Hence, CH1 IN,
CH3 IN, CH5 IN and CH7 IN are considered LO input channels.
The third wire connects to GND.
When should you use a differential mode configuration?
Differential input mode is the preferred configuration for applications in noisy
environments, or when the signal source is referenced to a potential other than PC
ground.
A low-noise precision programmable gain amplifier (PGA) is available on differential
channels to provide gains of up to 20 and a dynamic range of up to 16-bits.
In differential mode, the following two requirements must be met for linear operation:
Any analog input must remain in the
−
10 V to +20 V range with respect to ground
at all times.
The maximum differential voltage on any given analog input pair must remain
within the selected voltage range.
The input [
common-mode voltage
+
signal
] of the differential channel must be in the
−
10 V to +20 V range in order to yield a useful result.
For example, you input a 4 volt peak-to-peak (Vpp) sine wave to CHHI, and apply the
same sine wave 180° out of phase to CHLO. The common mode voltage is 0 V. The
differential input voltage swings from 4 V
-
(-4 V) = 8 V to -4 V
-
4 V = -8 V. Both inputs
satisfy the -10 V to +20 V input range requirement, and the differential voltage is suited
for the ±10 V input range (see Figure 4-5).
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