19
PW20i
HBM
A1269-2.0 en/de/fr
Multi-channel measurements are possible with a bus configuration using
PW20i load cells with an RS485 interface. All transducers on a line are
switched in parallel and are differentiated by the software assigning different
addresses. When the control computer has an RS232 interface, an interface
converter is required (e.g. HBM SC232/422B). The correct assignment of the
transmit and receive lines can be seen in Figure 7.3 (Bus line Ra to Ta of the
converter, etc.). The HBM converter and the PW20i both already contain bus
termination resistors. So no additional bus termination resistors are required.
Up to 32 PW20i can be connected to one bus.
The following must be noted when installing several PW20i’s in a system with
an RS-485 bus system:
The printed production number (identification plate) is required for setting up
data communication. If the identification plate can no longer be seen after
installation, the numbers of all PW20is should be noted beforehand. This
enables address assignment during the initial start-up.
Alternatively, before connection to the RS-485 line, each PW20i can be
individually connected to a PC in order to set different addresses (see
ADR-command, help file).
Fig. 7.3
Connecting several PW20i load cells to a computer via a 4-wire RS-485 bus
Wiring for the RS-485 version is similar, with lines RA, RB, TA, TB, GND and UB.
ATTENTION
The PW20i interface driver relates to GND. The Master interface driver
must also relate to this GND.
The PW20i already includes bus termination resistors. So no additional
bus termination resistors are required.