Data Translation DT9837, User Manual

Page: 84 / 150

Chapter 5
84
Phase Measurements – Tachometer Counter 1
On the DT9837A and DT9837B modules, you can measure the phase of the tachometer input
in relation to the A/D sample by reading tachometer counter 1. To read the value of this
counter, specify channel 5 in the analog input channel list.
An internal 48 MHz clock (with 21 ns resolution) is used to calculate the measurement, which
allows you to precisely correlate tachometer measurements with the analog input data.
You can specify the following parameters for tachometer counter 1 using the Open Layers
Control Panel applet, described on
page 36 , or by writing to the registers of the module, as
described in Appendix C starting on page 135 :
• The signal that starts the measurement: A/D sample, rising edge of the tachometer input
signal, or falling edge of the tachometer input signal
• The signal that stops the measurement: A/D sample, rising edge of the tachometer input
signal, or falling edge of the tachometer input signal
Note: 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.
• The value of the Self-Clear flag, which determines the value that is read between
measurements (either 0 or the previous measurement value)