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The "niDMM Is Overrange" Function Does Not Return a True Value When The Signal is Over Range

Primary Software: Driver Software>>NI-DMM
Primary Software Version: 2.5
Primary Software Fixed Version: N/A
Secondary Software: N/A
Hardware: Modular Instruments>>Digital Multimeters (DMM)>>PCI-4070, Modular Instruments>>Digital Multimeters (DMM)>>PXI-4070, Modular Instruments>>Digital Multimeters (DMM)>>PXI-4071

Problem:
I am using the NI-DMM driver and accidentally supplied a signal that's over the input range. Why doesn't the niDMM Is Overrange function return a true value when the signal is over range?

Solution:
In the NI-DMM driver, there are functions to check for over/under range conditions. They take a measurement value and determine if the value is a valid measurement or a value indicating that an over/under range condition occurred. The functions only look for "NaN" (Not a Number) or "-Inf" and return boolean values accordingly. Besides these functions, the driver also returns an over/under range warning to the error clusters.

Sometimes, the driver will still return the actual reading even though the signal is over/under range. For instance, when using the highest range of a 4070 and 4071, even readings at 105% of the maximum value will return the reading since most users will still want this value. As a result, the niDMM is Overrange function will not receive a "NaN" and therefore not return a "true" value. The overrange warning will be found in the error cluster.

The over/under range conditions are different for every DMM module, measurement type, and range. Some modules will return a "NaN" when the reading is above 100% of the range while others will return the actual reading until 130% over the range. To find out exactly what the over/under range conditions are for a specific module, please refer to the NI-DMM Help File: NI Digital Multimeters Help » Devices » NI 4072 » DMM Measurements » DMM Measurement Cycle »Overrange/Underrange

Related Links:
Product Reference: NI Digital Multimeters Help


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Report Date: 11/10/2005
Last Updated: 03/16/2007
Document ID: 3R9FGUIT

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