Handling High DC Voltages
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Caution All cables, connectors, and fixtures used in your system must have specifications to handle, with an adequate safety margin, 1000 V signals for the NI 4071 and 300 V signals for the NI 4065 and NI 4070/4072. |
The NI 4065 and NI 4070/4071/4072 inputs can measure sub-µV level signals with low drift, handle 300 (NI 4065 and NI 4070/4072) or 1000 (NI 4071) VDC and peak VAC signals, and recover very quickly for sub-µV level measurements in a system with switching. This ability is achieved through a flexible input protection design. Once the input exceeds about 15 V (NI 4070/4072) or 20 V (NI 4071) on the 10 V and lower ranges, the input protection triggers, and the input changes from a resistive characteristic to a constant current. This feature has the secondary benefit of reducing self-heating, so the DMM can recover rapidly to measure low-level signals with minimum recovery time.
However, you still need to consider that in a switching system where you are applying high voltages to a low range (for example, 300 V (NI 4065 and NI 4070/4072) or 1000 V (NI 4071) on the 10 V range), the switch receives a very short-duration current transient. The current transient does not cause any degradation effect on the NI 4065 and NI 4070/4071/4072. However, if the system switches an extreme overload to the DMM input mode with a moderate (tens of Hz) to high scanning rate over extended periods (weeks continuous or cumulative), the current transient can degrade the relay life in the switching system. For optimum switching system reliability when switching high voltages into any DMM, NI recommends selecting the range corresponding to the highest voltage expected.
Make sure that you do not exceed the V-Hz limit of the device, which is more likely to occur when measuring high-voltage/high-frequency signals; such action affects the internal transfer of data in the device and generates an error prompting you to reset the device and reconfigure the measurement.
Refer to Switching Voltages for recommendations on switching high voltages or signals with high common-mode voltage levels.
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Tip If the NI 4070/4071/4072 experiences the conditions where common-mode transients cause violation of the V-Hz limit of the instrument while the instrument is making measurements, the NI-DMM driver returns error NIDMM_ERROR_SERIAL_PORT_ERROR (defined as 0xBFFA401F, or -1074118625). If your system can potentially face this situation, your application should look for this error code after a call to:
Your application can handle this error by calling the following VIs or functions:
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