Campbell CR510, Operator'S Manual

Page: 107 / 264

SECTION 9. INPUT/OUTPUT INSTRUCTIONS
9-3
Every 0.125 seconds, the CR510 processor
transfers the values from the 8 (or 16) bit pulse
counters into 16 bit accumulators (max count is
65,535) and the counters are hardware reset to
zero. The pulses accumulate in these 16 bit
accumulators until the program table containing
the Pulse Count Instruction is executed. At the
beginning of the execution of the Table containing
the Pulse Count Instruction, the total in the 16 bit
accumulator is transferred to a temporary RAM
buffer. The 16 bit accumulator is then zeroed.
When the table execution reaches the Pulse
Count Instruction, the value in the RAM buffer is
multiplied by the multiplier and added to the offset
and placed into the designated input location. A
ramification of this is that the excitation interval of
the table must be short enough that the 16 bit
accumulator does not overflow.
CAUTION: The RAM buffer does NOT
accumulate counts; it is zeroed each time
the table is executed regardless of whether
or not the pulse instruction is executed. If
all counts are necessary, it is imperative
that the Pulse Count Instruction be
executed (not branched around) every time
the table is executed.
If a table execution was skipped because the
processor was executing the previous table
(Section 1.1.1) or if the user resets the time, the
value in the 16 bit accumulator is the result of a
longer than normal interval. This value can
either be used or it can be discarded. If pulse
counts are being totalized, a missing count
could be significant and the value from the
erroneously long interval should NOT be
discarded. If the pulse count is being
processed in a way in which the resultant value
is dependent upon the sampling interval (e.g.,
speed, RPM), the value from the excessive
interval should be discarded. If the value is
discarded the value in the RAM buffer from the
previous measurement will be used.
There is also an option to output the count as a
frequency (i.e., counts/execution interval in
seconds = Hz) as well as discard the result from
an excessive interval. This allows the use of a
conversion factor that is independent of the
execution interval.
The options of discarding counts from long
intervals, pulse input type, and using a 16 bit
counter are selected by the code entered for the
3rd parameter (Table 9-2).
NOTE: All pulse count instructions must be
kept in the same table. If the Pulse Count
Instruction is contained within a subroutine,
that subroutine must be called from Table 2.
TABLE 9-2. Pulse Count Configuration Codes
Code Configuration
0 High frequency pulse (Index (--) to
change from 8 Hz to 64 Hz reset)
1 Low level AC (Index (--) to
change from 8 Hz to 64 Hz reset)
2 Switch closure
3 High frequency pulse, sixteen
bit counter
4 Low level AC, sixteen bit counter
1X Long interval data discarded
2X Long interval data discarded,
frequency (Hz) output
where X is the configuration code
PARAM. DATA
NUMBER TYPE DESCRIPTION
01: 2 Repetitions
02: 2 Pulse channel or
Control Port number for
first measurement
03: 2 Configuration code
(from above table)
04: 4 Input location for first
measurement
05: FP Multiplier
06: FP Offset
Input locations altered: 1 per instruction
Intermediate storage locations altered: 1 per
repetition
*** 4 EXCITE, DELAY, AND MEASURE ***
FUNCTION
This instruction is used to apply an excitation
voltage, delay a specified time, and then make
a single-ended voltage measurement. A 1
before the excitation channel number (1X)
causes the channel to be incremented with
each repetition.
The 50 and 60 Hz rejection ranges (Section
13.1) do not have enough time between
integrations to allow a delay.