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When measuring resistance in a system, it is important to consider the effects of cable resistance. It is also important to notice that interactions between scanning multiple resistances and system cabling can present time-dependent problems. These problems can be avoided by following these simple guidelines.
The following figure illustrates the factors affecting settling time for a resistance measurement:
Settling Time = kCCRX
k = the value related to accuracy required
CC = the capacitance of the cable and switching network
RX = the resistance being measured
|Note Remember that if you measure 100 Ω on the 1 MΩ range, the settling time is a function of the measured resistance of 100 Ω, not 1 MΩ.|
Refer to the DMM Measurement Cycle section for more information on settling time. Remember that the Offset Compensated Ohms function toggles the current source on and off. Excessive system capacitance due to cables, in circuit elements, and so on may affect this measurement as it affects it in a scanning system. The Belden 83317E cable has a capacitance of 35.5 pF/ft and extremely low dielectric absorption. Refer to the Belden CDT Incorporated Web site at www.belden.com for information about this cable.