Function: Measurement Of Current - Siemens SIMATIC ET 200S Operating Instructions Manual

2PULSE
5.4 Modes and Functions
5.4.8

Function: Measurement of current

The measurement of current can be set in a variety of applications for control and
diagnostics purposes. You can read the measured value of the current from the feedback
interface.
Principle of operation
A measurement of current only takes place during the pulse output in the "Pulse width
modulation" and "Pulse train" operating modes. Without a pulse output (at
STS_ENABLE = 0), 0 is supplied as the measured value. The measured value is valid at
STS_ENABLE = 1.
In the "Pulse output", On/Off-delay" and "Frequency output" operating modes, 0 is always
measured as the measured value of the current.
The returned measured value of the current is a mean value of measured values that is
recorded during the duration of a period. At period durations < 5 ms, the interval between
two individual measuring points amounts to a maximum of 40 µs. When longer periods are
involved, 128 measuring points per period are always recorded. This results in
correspondingly longer intervals between the measuring points.
In isochronous mode, a new measured value of the current is always made available in the
feedback interface at the moment T
the current is made available about every 500 µs.
Note
In order for the current measurement to work correctly, no freewheeling diode may be
applied to the load.
Measuring range and measured value
The measuring range is set fixed to a rated current of 2 A.
The measured value of the current is supplied as a SIMATIC S7 analog value in the
feedback interface.
● A current of 2 A corresponds to the SIMATIC S7 analog value of 27648.
● With a parallel connection, a current of 4 A corresponds to the SIMATIC S7 analog value
Measurements of current are possible up to a SIMATIC S7 analog value of 32767. This
corresponds to a current of 2.4 A. Currents exceeding 2 A may only occur briefly.
Accuracy
The accuracy of the measurement of current amounts to 3% of the measuring range.
Note
This accuracy during current measurement can only be achieved if the time period is not
changed during the measurement.
310
of 27648.
. In non-isochronous mode, a new measured value of
i
Operating Instructions, 06/2010, A5E00124867-07
Technological Functions