ADLINK ACL-8454/12 - Manual (Page 42)

34 • Signal Connections & Applications
4.7 Frequency Measurement
Example : To measure frequency around 1~100 K Hz
step 1: This application needs two counters. One counter is used to
generate a pulse whose time interval is very precise. The pulse
is used to enable the other counter (counting counter) by gate
control. On ACL-8454, internal gate control is possible. The
internal gate is coming from /COUT6. In this example, the
pulse generate is counter #6 and the counter #1 is used to
measure frequency.
step 2: The maximum value of counting counter is no more than
65535. For measuring 100 K Hz frequency, the time interval
should be within 1/100 K Hz x 65535 = 0.655 sec. If the time
interval is wider then the measurement resolution is better,
however, if time interval is too long the counting value will be
overflow. That means the low pulse width of counter #6 output
should shorter than 0.655 sec. User can try to generate the
pulse by counter #6 by yourself.
step 3: Configure jumper ‘CK1’. The clock source is the signal to be
measured.
step 4~6: Skip these steps.
step 7: Set the internal jumper ‘G1’. The gate is controlled internally.
step 8: The following block diagram illustrates the application
step 9: Write and verify the control program. The frequency of the
signal is :
frequency = counting value of counter #1 / precise time
interval
Please refer the ‘DEMO4.C’ source code.