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MODBUS System Set Up
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There is one digital input counter for each input of the Model 1708 or Model 1716 RTU.
Each counter consists of two values: the count and the time period since the counter was last
cleared.
The count value increments each time the input activates. When the input is set up as status
mode, the count increments every time the input changes state. If the input is set up as
normally open or normally closed, the count increments when the input is grounded or
disconnected respectively.
The accumulators and counters are accessed through MODBUS holding registers. Each
accumulator or counter value (except for the accumulator sample rate) is spread across three
separate holding registers. The lower four decimal digits are in the first register, the middle
four decimal digits in the middle register, and the upper four decimal digits in the third
register. The example in Table 16 shows accumulator 1 with a current accumulated value of
2,156,349,078, number of samples of 634,127,890, and sample rate of 2,354:
Table 16. How Accumulator 1 Stores Data
Register
Value
Description
41011
9078
Accumulated Value lower four decimal digits
41012
5634
Accumulated Value middle four decimal digits
41013
0021
Accumulated Value upper four decimal digits
41014
7890
Number of Samples lower four decimal digits
41015
3412
Number of Samples middle four decimal digits
41016
0006
Number of Samples upper four decimal digits
41017
2354
Sample rate (the sample rate uses one register)
Some MODBUS software packages (e.g. WonderWare’s Intouch) can automatically combine
these registers into a single value. Others, (e.g. National Instrument’s Lookout) require the
user to combine the registers into a single value in a “script”. For example, in Lookout, the
“script” for the accumulated value might look like the following equation,
Queries to read an accumulator or counter must request all associated registers or an illegal
data address exception will be returned. An illegal data address exception will also be
returned to queries that overlap accumulator or counter address boundaries by requesting
more than nine registers.
Writing to the first holding register address used by particular accumulator or counter will
cause it to be cleared. The value written does not matter; the act of writing to the register
causes the clearing. It is not possible to clear just part of an accumulator or counter. For
example, you cannot clear the accumulator total without also clearing the number of samples.
Содержание 1708
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Страница 8: ...Contents 025 9209K 8...
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Страница 60: ...Repair 025 9209K 60 MODEL 1700 SERIES ENCLOSURE OUTLINE 024 0057B...
Страница 61: ...Repair 025 9209K 61 MODEL 1700 SERIES ENCLOSURE INSTRUCTIONS 024 0056D Sheet 1 of 2...
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Страница 63: ...Repair 025 9209K 63 MODEL 1708 REMOTE TERMINAL UNIT SILKSCREEN 702 9439F...
Страница 64: ...Repair 025 9209K 64 MODEL 1716 REMOTE TERMINAL UNIT SILKSCREEN 702 9440F...
Страница 72: ...Appendix B 025 9209K 72...
Страница 80: ...Glossary 025 9209K 80...