GE VMIVME-5550 Gas turbine control card

It depends on the length of the BTW. The module spends about 80µsec decoding each word of new data in binary. It takes twice as long to decode BCD. A worst case example of 64 words will take about 5.5msec in binary, and 11msec in BCD. These times start after the module receives the BTW. Don’t forget that it may take additional time based on changes in rate measurement sample periods. If you changed the sample period to 2 seconds, it will take an additional 2 seconds to receive a new frequency value.

Since the output indicator is tied to the control side of the module, it means that the module has commanded the output on. It does not necessarily mean that the output is on. The indicator illuminates even when no connection is made to the outputs or to the output supply. For an output to actually turn on, the output supply must be connected.

In rate measurement

 you select a time period in BTW words 21-24. The module will count pulses on channel A for this time period, and then convert the number to frequency. It will begin its next time period in about 10msec, and then begin counting pulses again. In period/rate or continuous/rate modes, the pulses coming in on the gate/reset will gate the internal 4MHz clock using the hardware scaler selected in words 21-24. If a scaler of 1 is selected, you are measuring the number of 4MHz pulses that occurred while the gate/reset was active, and the frequency returned will only be accurate if the incoming pulses occur with a 50% duty cycle.

With all other scaler values

 you are measuring the number of 4MHz pulses that occur in the scaler during a number of gate/reset periods that equal the the scalar value. For example, with a scaler value of 8, the 4MHz clock will be measured for four periods. The frequency value, 4MHz count ND bit and outputs will then be updated and remain constant as the counter is idle for the next four periods. Then the 4MHz clock will be measured for the next four periods and then be idle for four periods. Thus, the frequency is updated every eight periods. For more information, refer to appendix E.

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