8 VT1536A Isolated Digital Input/Output SCP
Output Voltage Clamp The output section incorporates a "crowbar" protection type voltage
clamping diode. In normal operation with the relay voltage at or below
56 Volts peak, the diode has virtually no effect (other than about
10 nanoamperes of leakage current). At 60 Volts , the diode starts to conduct
to limit further voltage excursions. In this r egion, the diode effectively
clamps momentary voltage spikes from inductive loads. If an overvoltage
condition occurs that drives a voltage surge in the diode to 80 Volts, the
diode will latch-on, clamping the voltage t o a few volts. This latched-on
condition will continue until the current surge through the diode is reduced
to less than 150 mA, whereupon the diode returns to its off state.
Debounce Function Setting the appropriate debounce period ensures that the VT1415A/19A
algorithm reads only the most current VALID digital input state as latched
into the SCP channel. By "valid" we mean that the signal has not made an y
0-to-1 or 1-to-0 transitions for the duration of the debounce period (the
signal has settled). If the algorithm read s a channel that has not yet settled,
it will receive the previously latched valid state (no change).
Debounce is controlled using VT1415A/19A SCPI commands. When the
debounce feature is enabled, inputs are tested for debounce, and valid sta tes
are latched every debounce periods. This debounce-and-latch rate is
Figure 4 The VT1536A Input and Output Sections
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