ABB REC 561, User Manual, Page: 40 / 643

Construction and hardware
characteristics - REC 561
ABB Network Partner AB
1MRK 580 148-XEN
Page 2 - 35
Version 1.0-00
2.6.4 mA input module
(MIM)
Up to six mA input modules that measure analogue current can be
included in a REC terminal. Each mA input module has six input chan-
nels, the channels are isolated from each other and have a separate A/D
converter. The transducer signals can be directly connected to the rear ter-
minals of the module.
2.7 Transformer input
module (TRM)
Current and voltage input transformers form an isolating barrier between
the external wiring and the internal circuits of the terminal. They adapt the
values of the measuring quantities to the static circuitry and prevent the
disturbances to enter the terminal
You can connect 10 analogue input quantities to the transformer module
that consists of:
• Five voltage transformers that cover a rated range from 100 to
125 V.
• Five current transformers in two versions - one for 1 A and one for
5 A rated current.
2.8 A/D-conversion
module (ADM)
The incoming signals from the intermediate current transformers are
adapted to the electronic voltage level with shunts. To gain dynamic range
for the current inputs, two shunts with separate A/D channels are used for
each input current. So a 16-bit dynamic range is obtained with a 12 bits
A/D converter.
The next step in the signal flow (see Fig. 2) is the analogue filter of the
first order, with a cut-off frequency of 500 Hz. This filter is used to avoid
aliasing problems.
The A/D converter has a 12-bit resolution. It samples each input signal (5
voltages and 2
.
5 currents) with a sampling frequency of 2 kHz.
Before the A/D-converted signals are transmitted to the main processing
module, the signals are band-pass filtered and down-sampled to 1 kHz in
a digital signal processor (DSP).
The filter in the DSP is a numerical filter with a cut-off frequency of
250 Hz.
The transmission of data between the A/D-conversion module and the
Main processing module is done on a supervised serial link of RS485 type.
This transmission is performed once every millisecond and contains infor-
mation about all incoming analogue signals.