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Parent Topic: Learn More about Device Fundamentals
Symptoms of Issue:
Possible Cause: The time-domain data from which NI InsightCM Server calculates the features might not be of a sufficient duration. To calculate features from integrated data, NI InsightCM Server requires enough time-domain data to allow for filter settling time.
As mentioned previously, this issue occurs only when single or double integration is enabled for a channel. Also, the issue often occurs in data acquired as part of a run-up or coast-down stream because those acquisitions can be very short. For example, consider a device configured to perform stream acquisitions with a length of 10 revolutions. For fast-moving equipment, the revolutions might occur in a very short amount of time, meaning the resulting waveforms do not contain enough data for NI InsightCM Server to calculate feature values.
This issue can still occur even if you ensure that acquisitions always last at least one second. For example, consider an accelerometer channel with single integration enabled in order to perform velocity measurements. If features calculated from the acceleration data are valid but velocity features have error values, the cause might be that the velocity time-domain data is too short. This occurs because of the way NI InsightCM Server filters integrated time-domain data.
To account for integration settling time, NI InsightCM Server discards the first n seconds of the integrated time-domain data before calculating features from it, where the following equation determines the value of n.
n = (1 / Integration Cutoff) * x
As the following table explains, the value of Integration Cutoff and x vary according to whether NI InsightCM Server performs single or double integration.
|Type of Integration||Source of Integration Cutoff Value 1||Value of x Constant|
|Single||Single Integration Cutoff property||3|
|Double||Double Integration Cutoff property||10|
|1 You can set these properties for each channel on the Device Configuration page»Channels tab»Properties sub-tab.|
For example, consider a channel with single integration enabled that acquires data for 1.5 seconds during a stream acquisition. NI InsightCM Server filters the single-integration waveform according to the following equation.
1.0 = (1 / 3) * 3
NI InsightCM Server discards the first 1.0 second of filtered, unsettled time-domain data. In other words, the integrated time-domain data spans only 0.5 seconds, which is not sufficient for NI InsightCM to calculate features.
To avoid situations where integrated time-domain data is too short, set the acquisition duration to be a number of seconds such that the waveform is at least one second longer than the integration filter settling time.
Also, if you change the value of the Single Integration Cutoff or Double Integration Cutoff property for a channel, ensure the new value does not cause the integration settling time to become too long.
Complete the following steps to change the value that NI InsightCM Server uses to represent errors: