Measurement Computing Data Translation DT9857, User Manual

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Principles of Operation
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Measure Counter Features
DT9857 and DT9857E modules provide two measure counters (counters 1 and 2). Using these
counters, you can measure the frequency, period, or pulse width of a single signal or the time
period between two signals and return the value in the analog input stream. This is useful for
correlating the analog input data with digital positional data, measuring the frequency of a
signal, or as a tachometer. An internal 48 MHz counter is used for the measurement, yielding a
resolution of 20 ns (1/48 MHz).
To use measure counter 1, specify channel 10 for the DT9857-08 and DT9857E-08 module, or
channel 18 for the DT9857-16 or DT9857E-16 module in the analog input channel list. To use
measure counter 2, specify channel 11 for the DT9857-08 or DT9857E-08 module, or channel 19
for the DT9857-16 or DT9857E-16 module in the analog input channel list.
Using software commands, you can configure the following parameters for counter 1 and/or
counter 2:
• The operation mode as continuous edge-to-edge measurement mode.
• The signal that starts the measurement. The following signals are supported:
−
A/D conversion complete
−
Tachometer input falling edge
−
Tachometer input rising edge
−
Digital input 0 falling edge
−
Digital input 0 rising edge
−
Digital input 1 falling edge
−
Digital input 1 rising edge
−
Digital input 2 falling edge
−
Digital input 2 rising edge
−
Digital input 3 falling edge
−
Digital input 3 rising edge
−
Digital input 4 falling edge
−
Digital input 4 rising edge
−
Digital input 5 falling edge
−
Digital input 5 rising edge
−
Digital input 6 falling edge
−
Digital input 6 rising edge
−
Digital input 7 falling edge
−
Digital input 7 rising edge
−
C/T 0 Clock input falling edge
−
C/T 0 Clock input rising edge
−
C/T 0 Gate input falling edge