Campbell Scientific AM416 Multiplexer - Manual (Page 13)

AM416 RELAY MULTIPLEXER
7
(3) Clock/Delay - With the CR10(X), the clock
line is connected to a control port. Instruction
86 with the pulse port command (71- 78), sets
the clock line high for 10 ms. Instruction 22 is
used to delay an additional 10 ms.
When controlled by the 21X or CR7, the clock
line may be connected to either an excitation or
a control port. Connection to an excitation port
is preferred because only one instruction (22) is
required to send the clock pulse. Instruction 22
should be programmed to provide a 10ms delay
with a 5000mV excitation. A control port can be
used to clock the AM416 if no excitation ports
are available. The 21X and CR7 instruction
sequence required to clock with a control port
is: Instruction 20 (set port high), Instruction 22
(delay of 20 ms without excitation) followed by
Instruction 20 (set port low).
(4) Step Loop Index - This instruction is used
when a measurement instruction within that
loop has more than one repetition. It allows
each measurement value to occupy a
sequentially assigned input location without
being overwritten by subsequent passes
through the loop. Without this instruction, each
indexed input location within the loop will
advance by only one location per loop iteration.
For Example: 2 sensors per SET, 6 sensors
total; two reps in measurement instruction; two
measurement values assigned to indexed input
locations (--); P90 step of 2. Loop count of
three.
Input locations
1 2 3 4 5 6
First pass: 1 2
Second pass: 3 4 sensor
Third pass: 5 6 numbers
Given the same program without a step loop
instruction, the following situation results:
Input locations
1 2 3 4 5 6
First pass: 1 2
Second pass: 3 4 sensor
Third pass: 5 6 numbers
The measurement values for the 2nd and 4th
sensors will be overwritten in their input
locations. The 1st, 3rd, 5th, and 6th
measurement values will reside in the first 4
input locations.
The Step Loop Instruction 90 is available in
CR10(X)s, CR7s, and 21Xs with a third PROM.
For 21X dataloggers without a third prom (i.e.
without Instruction 90), a separate
measurement instruction (with one rep) is
required for each sensor measured within the
loop. The input location parameter within both
measurement instructions is indexed.
For Example: 2 sensors per SET; one rep in
each of two measurement instructions; two
measurement values assigned to indexed input
locations (--), one begins with input location 1,
the other with input location 4; no P90. A total
of six sensors to be measured; loop count is
three.
Input locations
1 2 3 4 5 6
First pass: 1 2
Second pass: 3 4 sensor
Third pass: 5 6 numbers
A potential drawback of this technique is that
sequential sensors (i.e. those input to the same
SET) will not have sequential input locations.
(5) Measure - Enter the instruction needed to
measure the sensor(s) [see Section 6, Sensor
Hook-Up & Measurement Examples]. The input
location parameter of a measurement
instruction is indexed if a (--) appears to the
right of the input location. Index an input
location by pressing "C" after keying the
location. Indexing causes the input location to
be incremented by 1 with each pass through the
loop. This allows the measurement value to be
stored in sequential input locations. Instruction
90, as explained above, allows the indexed
input location to be incremented in integer steps
greater than 1.
NOTE: If more than 28 input locations are
utilized, then additional input locations must
be assigned using the datalogger *A mode.
Consult your datalogger manual for details.
(6) Optional Processing - Additional processing
is sometimes required to convert the reading to
the desired units. It may be more efficient or
reduce measurement time if this processing is
done outside the measurement loop. A second
loop can be used for processing, if necessary.