NetDAQ Users Manual

Noise, Shielding, and Crosstalk Considerations
Crosstalk Considerations B
B-3
the routing of your input wiring: keep it away from or shielded from all ac
power mains wiring and other sources of noise.
3. Channel Spacing When possible, leave as many unused channels as possible
between your ac voltage channel inputs and your low level inputs.
Crosstalk from a VAC or frequency signal on a 2645A channel to an adjacent
channel using the Slow reading rate is as shown in Table B-1:
Table B-1. 2645A Crosstalk Specifications.
VAC/Frequency Volts DC Resistance
Temperature
(100 Ohm RTD)
Temperature
(Thermocouple)
<100 Hz -80 dB .2%/V if R>3k .04°/V .1°/V
100 Hz -100 dB .1%/V if R>3k .02°/V .003°/V
500 Hz -100 dB .1%/V if R>3k .02°/V .03°/V
1 kHz -50 dB .1%/V if R>3k .02°/V .3°/V
2 kHz -60 dB .05%/V if R>3k .02°/V .1°/V
5 kHz -66 dB .1%/V if R>3k .02°/V .1°/V
10 kHz -80 dB .01%/V .02°/V .1°/V
20 kHz -50 dB .02%/V .05°/V .1°/V
50 kHz -40 dB .05%/V .1°/V .5°/V
100 kHz -40 dB .1%/V .2°/V 1°/V
>100 kHz -40 dB .1%/V .4°/V 2°/V
Note 1 The temperature ranges are particularly susceptible to crosstalk at frequencies above 20
kHz, and that the error goes up as the square of the voltage, e.g., 2V ac at 100 kHz can cause a
4 degree error on a thermocouple. Because of this sensitivity, it is not advisable to mix
temperature signals and high frequency signals in the same 2645A.