13
14063434.02 10/2019 EN/DE
WIKA operating instructions transmitter, models GDT-20, GDHT-20
EN
6. Commissioning, operation
Interferences in the differential mode can be compensated by a network of decoupling capaci
-
tors that are located in front of the read-out unit.
6.2.4 RS-485
The physical layer the for Modbus
®
protocol is the serial RS-485 interface per EIA/TIA-485.
Herefore, the differential signal between pins 4 and 5 (A and B) is evaluated with a 2-wire
system (half-duplex). The mutual reference potential for the signals is on pin 1 (C).
6.3 Modbus
The Modbus
®
communication protocol is based on a master/slave architecture. The protocol
implemented in the transmitters GDT-20 and GDHT-20 is Modbus
®
RTU with serial transmis-
sion via a 2-wire RS-485 interface.
The Modbus
®
protocol is a single-master protocol. This master controls the entire data and
monitors any possible timeouts (no reply from the addressed instrument). The connected
instruments may only send telegrams after request by means of the master.
Modbus
®
RTU (RTU:
R
emote
T
erminal
U
nit) transmits the data in binary form, guaranteeing a
good data throughput.
Detailed information on the protocol under www.Modbus.org
6.4 Modbus
®
startup kit
The transmitter with the optionally available startup kit (order no. 14075896) can be configured
at the measuring point for operation.
Differential mode interferences
T-connector
Transmitter
Gas Compartment
