Measurement Computing WaveView - Manual (Page 22)

WaveView, pg. 20 03-05-02 WaveView
Edge Type
– Applies to WBK17 Only. The Edge Type column is used to set the edge to be detected
as a “Rising” or “Falling” edge. Each WBK17 channel’s edge type setting is independent of the settings for
the other channels.
Debounce Time
– Applies to WBK17 Only. Each WBK17 channel has its own programmable
debounce module. The modules can be used to eliminate switch-induced transients that are typically
associated with electro-mechanical devices including relays, proximity switches, and encoders. The
16 possible selections for debounce time reside within the range of 500ns to 25.5ms [inclusive].
Debounce times should be set according to the amount of instability expected in the input signal. Setting a
debounce time that is too short may result in unwanted glitches clocking the counter. Setting a debounce
time too long may result in an input signal being rejected entirely. Some experimentation may be required
to find the appropriate debounce time for a particular application.
To see the effects of different debounce time settings, simply view the analog waveform along with the
counter output.
Reference Note:
Refer to the
Debounce Module section of the WBK17 Document Module for additional
information.
Debounce Edge Detection
– Applies to WBK17 Only. The Debounce Edge Detection column
allows for one of two debounce trigger-mode selections. These are: (1) after stable, and (2) before stable.
The “trigger after stable” mode behaves like a traditional debounce function, i.e., rejecting glitches and
only passing state transitions after a specified period of stability (the debounce time). Trigger after stable
mode is used with electro-mechanical devices like encoders and mechanical switches to reject switch
bounce and disturbances due to a vibrating encoder that is not otherwise moving. The debounce time
should be set short enough to accept the desired input pulse but longer than the period of the undesired
disturbance.
In the “trigger before stable” mode, the output of the debounce module immediately changes state, but will
not change state again until a period of stability has passed. For this reason the mode can be used to detect
glitches.
Use the trigger before stable mode when the input signal has groups of glitches and each group is to be
counted as one. The trigger before stable mode will recognize and count the first glitch within a group but
reject the subsequent glitches within the group if the debounce time is set accordingly. In this case the
debounce time should be set to encompass one entire group of glitches.
Reference Note:
Refer to the
Debounce Module section of the WBK17 Document Module for detailed
information.
Tick Duration
– Applies to WBK17 Only. The “tick duration,” also referred to as “ticksize,” is a
fundamental unit of time. WaveView’s Tick Duration column permits four possible settings: 20ns, 200ns,
2000ns, 20000ns. For measurements that require a timebase reference, such as period or pulsewidth, the
ticksize is the basic unit of time. The count value returned in the scan is the number of ticks that make up
the time measurement.
Reference Note:
Refer to the
WBK17 Document Module for explanation on how the tick duration affects the
range for period, pulsewidth, and timing modes.