A few terms related to noise rejection and which are used in eZ Analyst and eZ

A few terms related to noise rejection and which are

This preview shows page 69 - 71 out of 122 pages.

configuration is made via eZ-Analyst or eZ-TOMAS software. A few terms related to noise rejection, and which are used in eZ-Analyst and eZ-TOMAS, are: Edge Detect Edge Detect is short for “Tach Pulse Edge Detection.” The term pertains to detecting the rising or falling edge of a tachometer pulse using either an “Immediate” or “Delayed” mode. Immediate Edge Detection (“Before Stable”) “Immediate” is one of two Edge Detect modes. The term is synonymous with “ Before Stable .” If “Immediate” edge detection is selected a tach pulse will be recognized on any instantaneous measurement that meets the trigger level criteria. In this setup the “Delay Value” is the amount of time before the next tach pulse can be recognized. If a keyway is being used as a tach trigger you must calculate the minimum pulse width, based on the maximum RPM rate expected. Delayed Edge Detection (“After Stable”) “Delayed” is one of two Edge Detect modes. The term is synonymous with “ After Stable .” If “Delayed” edge detection is selected a tach pulse will be recognized when the measurement meets the trigger criteria for the specified duration. In this setup the “Delay Value” defines the length of time that the trigger criteria must be stable before the tach pulse will be recognized. From the following illustration we can see that there are two debounce modes, as well as a debounce bypass. In addition, the signal from the comparator can be inverted before it enters the debounce circuitry. The inverter is used to make the input rising-edge or falling-edge sensitive. Edge selection is available with or without debounce. In this case the debounce time setting is ignored and the input signal goes straight from the inverter [or inverter bypass] to the counter module. There are 16 different debounce times. In either debounce mode, the debounce time selected determines how fast the signal can change and still be recognized. Debounce Model ZonicBook/618E 917695 Tach Channels 7-5
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Trigger After Stable (“Delayed Edge Detection”) Mode In the “Trigger After Stable” mode, the output of the debounce module will not change state until a period of stability has been achieved. This means that the input has an edge and then must be stable for a period of time equal to the debounce time. Debounce Module – Trigger After Stable Mode “Delayed Edge Detection” The following time periods (T1 through T5) pertain to the above drawing. In Trigger After Stable mode, the input signal to the debounce module is required to have a period of stability after an incoming edge, in order for that edge to be accepted (passed through to the counter module.) The debounce time for this example is equal to T2 and T5. T1 In the example above, the input signal goes high at the beginning of time period T1 but never stays high for a period of time equal to the debounce time setting (equal to T2 for this example.) T2 – At the end of time period T2, the input signal has transitioned high and stayed there for the required amount of time, therefore the output transitions high. If the Input signal never stabilized in the high
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