Campbell Scientific CR23X Micrologger - Manual (Page 151)

SECTION 9. INPUT/OUTPUT INSTRUCTIONS
9-17
*** 26 TIMER ***
FUNCTION
This instruction will reset a timer or store the
elapsed time registered by the timer in seconds in
an Input Storage location. Instruction 26 can be
used with Program Control Instructions to measure
the elapsed time between specific input conditions.
There is only one timer and it is common to all
tables (e.g., if the timer is reset in Table 1 and later
in Table 2, a subsequent instruction in Table 1 to
read the timer will store the elapsed time since the
timer was reset in Table 2).
Elapsed time is tracked in 0.1* second
increments. The maximum interval that can be
timed is 46.6 days.
The timer is also reset in response to certain
keyboard entries:
1. When tables are changed and compiled
with the
0 Mode, the timer is reset
automatically.
2. Entering "
∗
6" after changing the program
compiles the programs, but does NOT reset
the timer.
PARAM. DATA
NUM. TYPE DESCRIPTION
01: 4 Input location no. of
elapsed time in seconds
(or enter 0 to reset)
Input locations altered: 1
(0 if timer is being reset)
*** 27 PERIOD AVERAGE (SE) ***
FUNCTION
Instruction 27 measures the period
(microseconds) of a signal on a single-ended
input channel. As an option, the frequency of
the signal in kHz may be output instead of the
period.
The number of cycles to measure should be
chosen so that at least 1.1 milliseconds
transpires while counting those cycles (e.g., if
the maximum input frequency is 10 kHz, choose
at least 11 cycles to be measured). If the time
for the number of cycles is less than 1.1
milliseconds, an overrange value (displayed as -
99999) will be stored for the measurement. The
specified number of cycles are timed with a
resolution of 12 nanoseconds, making the
resolution on the period 12 nanoseconds
divided by the number of cycles measured.
The “Time out” parameter specifies the
maximum length of time the instruction will wait
on each repetition for the specified number of
cycles. If the cycles have not been counted
within this time, -99999 will be loaded into the
input location.
TABLE 9-8. Period Average Output Options/Range Codes
Range
Code
Voltage
Gain
Minimum
Signal (pk-pk)
1
Maximum
Signal (pk-pk)
1
Minimum
Pulse Width
Maximum
Frequency
2
x4 1.0 500 mV 10.0 V 2.5
µ
s 200 kHz
x3 5.0 40 mV 2.0 V 10
µ
s 50 kHz
x2 20 5 mV 2.0 V 62
µ
s 8 kHz
x1 100 2 mV 2.0 V 100
µ
s 5 kHz
x = 0 Output Period in
µ
s x = 1 Output frequency in Hz
1 - Signals must be centered around datalogger ground to trigger zero-crossing detector.
2 - Maximum frequency equals 1/(Twice Minimum Pulse Width) for 50% duty cycle signals.