
13/89 Device handbook A
PLUS
with / without LED display
,
157
679-19, 04/2016
3.4 Free Modbus image
Accessing measured data of a Modbus device often needs some special effort, if the interesting
measurements are stored in different, non continuous register areas. This way multiple telegrams must be
sent to the device to read all data. This needs time and it's very likely, that the measurements don't
originate from the same measurement cycle.
A free assembly of the data to read helps a lot. The A
PLUS
supports, along with the still available classical
Modbus image with thousands of registers, the facility to assemble two different images, which may be
read with one telegram only. These freely assembled images are refreshed after each measurement cycle
and therefore always provide the most present values.
The free float image
Up to 60 instantaneous, mean, unbalance or THD/TDD values may be arranged in any sequence on the
register addresses 41840-41958. All of these values are floating point numbers, which allocate 2 registers
per value. Meter values are not possible because they have another format.
The free integer image
Some older control systems are not able to handle float values. To make it possible to work with the data
of the device up to 20 16-Bit integer values can be derived from the existing measurement values. These
values will then be stored in the free Modbus image (register 41800 up to 41819) as integer values with
selectable range of values.
Example
: Current transformer 100/5A, measurement current phase 1, over range 20%
► The reference value is 120A (maximum measurable current)
► The integer value shall be 12'000 if the measurement is 120A
After selecting the measured quantity and entering the register value of 12'000 automatically a scaling
factor of 100.0 is calculated. The measurement I1 therefore will be multiplied by 100.0 before it is
converted into an integer value and stored in the Modbus image.
Also in the integer image instantaneous, mean, unbalance or THD/TDD values may be arranged.
For devices with Profibus interface the Modbus image is used for the assembly of the
cyclical telegram. Via Modbus the same image can be used, but it’s not possible to use it
independently.
The Modbus communication of the A
PLUS
is described in a separate document. Depending on the
communication hardware selected, either the manual for Modbus/RTU or Modbus/TCP protocol should be
used. These documents can be downloaded via our homepage
http://www.camillebauer.com
.
► W157 695: Modbus/RTU interface A
PLUS
(communication interface RS485)
► W162 636: Modbus/TCP interface A
PLUS
(communication interface Ethernet)