Data Translation DT9837, User Manual

Page: 37 / 150

Setting Up and Installing the Module
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7. You can read the number of counts between two consecutive starting edges of the
tachometer input signal by including channel 4 (tachometer counter 0) in the analog input
channel list. On the DT9837 module, the starting edge is always rising; on the DT9837A
and DT9837B modules, the starting edge is programmable (either rising or falling). See
page 82 for more information.
For the DT9837, skip to step 11. For the DT9837A and DT9837B modules, configure the
Tach.CT0 measurement parameters as follows:
a. From the Start Select combo box, select the edge ( Rising Edge or Falling Edge ) of the
tachometer input signal that you want to use to start the measurement.
b. From the Measure Mode combo box, select Zeros if you want to read a value of 0
between measurements, or select Previous Measurement if you want to read the
previous measurement value if the new measurement value is not yet complete.
c. From the Stale Data combo box, select Used if you want to indicate whether or not
the measurement value if new, or select Not Used if you do not want to indicate
whether the measurement value is new. If you select Used , the most significant bit
(MSB) of the measurement value is set to 0 when the value is new and set to 1 when
the measurement is not yet complete. If you select
Not Used , the MSB of the
measurement value is always 0.
8. On the DT9837A and DT9837B modules, you can measure the time from the stopping
edge of the tachometer input signal to the A/D sample or from the A/D sample to the
stopping edge of the tachometer input signal by specifying channel 5 (tachometer counter
1) in the analog input channel list; see
page 84 for more information. Configure the
Tach.CT1 measurement parameters as follows:
a. From the Start Select combo box, select the signal that you want to use to start the
measurement ( A/D Sample , Tach Input Rising Edge , or Tach Input Falling Edge ).
b. From the Stop Select combo box, select the signal that you want to use to stop the
measurement ( A/D Sample , Tach Input Rising Edge , or Tach Input Falling Edge ).
Note that if you choose to start the measurement using the A/D sample, choose a
tachometer edge to stop the measurement. Likewise, if you choose to stop the
measurement using the A/D sample, choose a tachometer edge to start the
measurement.
c. From the Self Clear combo box, select Clear to zero if you want to return a value of 0
between measurements, or select Keep last Value if you want to return the previous
measurement value between readings.