Ametek VTI Instruments EX1200-1538, User Manual

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VTI Instruments Corp.
30 EX1200-1538: Counter/Timer Operation
Tooth Period
= 50 ms
Averaging Window Averaging Window
RPM=100 RPM=100
Tooth Count=12
Tooth
Count=12
A
B
F
IGURE
3-17: N
OMINAL
T
OOTH
C
OUNT FOR
RPM M
EASUREMENTS
When using the RPM function, ramp up time, ramp down time, and derivative parameters, such as
acceleration, deceleration, etc., can be measured by tweaking the averaging window, sample
trigger, etc.
Time Interval Measurement
Time Interval , or pulse-edge separation, measurements determine the time elapsed between the
transition states of two signals on two different channels as shown in Figure 3-18. When the Slope
of the signal is set to Positive , the Time Interval function uses the positive-going state transition,
while the negative transition state is used when the Slope parameter is Negative . Since the Time
Interval function is comparative, one channel must be defined as the Reference channel while the
other channel is referred to as the Measurement channel. If a Measurement channel is not
defined, the EX1200-1538 automatically uses the next adjacent channel as the reference channel.
If the input signal is not present or if the input signal does not crosses the configured threshold
limit, the measurement will be waiting continuously for the signal. To prevent this,
Aperture
Time should be defined for this measurement, so that the instrument indicates the averaged
measurement reading (if at least one complete measurement was acquired) and resets itself at the
end of each aperture time window.
Reference
Channel
Measurement
Channel
T
1
T
2
Time Interval Result in the Last Aperture Window = (T
1
+T
2
)/2
Aperture Time Window
F
IGURE
3-18: T
IME
I
NTERVAL
M
EASUREMENTS
The initial time interval measurements are always based on the first pulse detected on Reference
channel. Should one or more pulses occur on the Reference channel prior to the first pulse
occurring on the Measurement channel, the time interval value returned will be the time between
the first pulse on the Reference channel and the first on the Measurement channel. If any pulses
occur on the Measurement channel prior to the first pulse on the Reference channel, these pulses
are ignored. If multiple pulses occur in the aperture window on both the Reference and
Measurement channels, the average of these time intervals will be returned as the result of the