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Voltmeter Time Constant

Controls: Options >> Voltmeter >> TC
Macro: VoltTC

This controls the rate at which Voltmeter values can change. If the actual data values are jumping around due to noise, they can be hard to read. The time constant (TC) controls an exponential smoothing operation on the stream of changing values, so that the display shows an average value over time.

Voltmeter TC settings may range from 0 to 31, where 0 is no smoothing at all: In that case, the display changes immediately when the voltage changes. The default setting is 5.

If the true voltage changes suddenly, the display may exhibit a lag before settling to a new average. This becomes more of a problem at large TCs, so you must select a TC that is a compromise between a jittery display on noisy data, and lagging response on true voltage changes.

The TC value can be converted to an approximate time constant (seconds) by multiplying the effective trace update interval by 2^TC. This may be useful for comparison with Response Time values of the Sound Level Meter, which are given in milliseconds.

For TC = 5 (default), 2^5 = 32. So if the update interval is 17 msec (a typical value), the effective time constant would be 32 * 17 = 544 msec.

The update interval is smallest when the Trace Update interval is set to minimum, and when Trigger is off. The actual update interval also includes time for processing and displaying data. You can obtain the actual update interval from the Sgram/PT X-axis extent, divided by 512 updates per Sgram screen.

Note: The Voltmeter display freezes in Pause mode, showing the most recent instantaneous value, not the time-constant output. You can toggle to other Voltmeter modes (RMS, dB, Pk Hold, etc) while Paused, to see their most recent values.

Macro Notes:

VoltTC=5 sets the TC to 5. VoltTC=>1 increments and VoltTC=>-1 decrements the TC.

See also Voltmeter, Voltmeter Channel, Sound Level Meter Response Time, Cursor Time Constant (TC)


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