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Appendix A. Single-Ended Measurements

A-5

FIGURE A-2. Single-Ended Measurement

A.2 Indexing with Loops

When a multiplexer is measured with a measurement instruction within a loop, the

input locations in which to store measurements must be indexed to the loop

counter so the measurement is stored in the next input location each pass through

the loop. When more than one repetition is used on the measurement instruction,

as in examples A-1 and A-2, Instruction 90 is used to set the increment of the loop

index. With Instruction 90 correctly used, each measurement will occupy its own

input location, without being overwritten by subsequent passes through the loop.

Take the following measurement case. Six Type T thermocouples are measured

with a CR10 and AM25T. The thermocouples are wired into the AM25T as

shown in Figure A-1. Instruction 13, with two repetitions, is used to measure the

thermocouples inside a loop. With a Loop Count of three and no indexing on the

thermocouple location (Example A-3), the measurements would be stored in

Input Storage as shown in Table A-1.

Note that after the third pass through the loop, only the last two measurements

are in Input Storage. The temperatures for TC_1 through TC_4 have been

overwritten.

The multiplexer control instructions are not included in the

example program fragment.

TABLE A-1. Values in Input Storage; Input Location Not Indexed

Pass 18 19 20 21 22 23

First TC_1 TC_2

Second TC_3 TC_4

Third TC_5 TC_6

When the Input Location is indexed (see Instruction 87 in the datalogger

manual), the Loop Index counter is added to the specified input location, each

pass through the loop, to determine where the measurement is stored. By

default, the index advances by one with each pass through the loop. Simply

indexing a measurement instruction’s Input Location works, when the

NOTE

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Campbell AM25T Spezifikationen Seite 29