Instructions

4 Configuration and programming
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With the option "4-20 mA", a 121 Ω shunt resistor is connected to each channel.
– Lower measuring limit – minimum level of the input signal
– Upper measuring limit – maximum level of the input signal.
The lower and upper measuring limits must be set to scale the input signal.
– Decimal point offset (DP) – The input value is saved as REAL32 and INT16 in the device
Modbus register. Decimal point offset determines the decimal point shift to the right while saving
the input value as INT16. For instance: If the input value is 3.14 and the offset is 1, then 31 will be
written in the INT16 register.
4.3.2 Digital mode
Configurable parameters:
– Input mode – select Digital
– Debouncing filter – filter time constant (sect. 4.3.3)
– LOW – switching threshold from HIGH to LOW, can be adjusted in ALP in the range 2.5…10 V
and should be lower than HIGH level by at least 0.5 V
– HIGH – switching threshold from LOW to HIGH, can be adjusted in ALP in the range 3.0…10.5 V
and should be higher than logical LOW level by at least 0.5 V
The input operates as a comparator with parameters LOW and HIGH which determine the
hysteresis.
Abb. 4.3 Digital mode of an analog input
The input state will not change, until the input voltage is within the dU interval. To avoid the ambiguity
of determining the input state, the parameter HIGH must be set higher than the parameter LOW by
at least 0.5 V.
4.3.3 Analog filter
The input filter stabilizes the input reading. The filter parameter is a time constant representing the
time interval in which the signal reaches 0.63 of the measured value. It can be set within the range of
0.01…60 s for each input separately.
The greater the time constant, the higher the damping of the interference signal and the slower the
reaction to rapid changes in the input value.
4.4 RS485 interface
PR100 uses the common standard RS485 for data exchange. RS485 serial interface is based on
two-wire technology and half-duplex mode. Protocols Modbus RTU / ASCII are supported, with
automatic protocol detection.
The network consists of a master device and up to 16 slaves. The maximum length is 1200 m. The
number of slave devices and the network length can be increased using a RS485 interface repeater.
Devices are connected to a network according to linear (bus) topology. It means that the line goes
from the first device to the second one, from the second one to the third one, etc. Star connections
and spur lines are not allowed. Line reflections always occur at the open bus ends (the first and the
last node). The higher the data transmission rate, the stronger they are. Terminating resistors are
sometimes needed to minimize reflections. Experience proves that the most efficient practice is to
use terminating resistors of 150 Ω.