Progress Direct Systems Volt Tattler 2 Owner's Manual page 23

T (Tone) is being generated if the speaker is sounding.
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Morse may show up on an analog voltmeter as the needle moving up and down when tones
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sound.
OK_Pulse indicates that the unit is operating and taking samples.
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Hi_Pulse indicates that a high threshold transition has occurred since VT2 was powered on or
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reset by a momentary press of the Programming Button.
Low_Pulse indicates that a low threshold transition has occurred since VT2 was powered on or
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reset by a momentary press of the Programming Button.
Hyst goes low at reset or power up. It will go high if a high voltage transition occurs. It will
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remain high until reset or until a low transition occurs. Hyst takes the state of the last transition
crossed since reset or power on.