Mettler Toledo IND780 Installationshandbuch Seite 54

Connections
TO AVOID DAMAGE TO THE PCB OR LOAD CELL, REMOVE POWER FROM THE IND780
TERMINAL AND WAIT AT LEAST 30 SECONDS BEFORE CONNECTING OR DISCONNECTING
ANY HARNESS.
When using the IND780 with one or more analog load cells, load cell connections
are made to the connector located on the Analog Load Cell option board. The 7-
position connector is visible at top right in Figure 2-39, with the board's 2-position
discrete output connection next to it. Note that for clarity the board's socket is
shown with two (unwired) connectors plugged into it.
When installing Analog Load Cell boards, to prevent electromagnetic
interference twist the connector wires before attaching the connector to the
board.
Analog Load Cell boards may be placed in any of slots 1 through 4, for a total of
four scales. The IND780 can power as many as 16 load cells.
The IND780 terminal is designed to power up to eight 350-ohm load cells (or a
minimum resistance of approximately 43 ohms) per card. To confirm that the load
cell load for this installation is within limits, the total scale resistance (TSR) must
be calculated. To calculate TSR:
TSR =
Ensure that the TSR of the load cell network to be connected to the IND780 has a
resistance greater than 43 ohms before connecting the load cells. If the resistance
is less than 43 ohms, the IND780 will not operate properly.
In addition, the maximum cable distance must be reviewed. Table 2-7 provides
recommended maximum cable lengths based on TSR and cable gauge.
Table 2-7: Recommended Maximum Cable Lengths
TSR (Ohms)
(meters/feet)
350
87 (4-350 Ω cells)
43 (8-350 Ω cells)
Figure 2-41 shows wiring definitions for the analog load cell connector. Note that
when using four-wire load cells, jumpers must be placed between the +Excitation
and +Sense terminals and between the Excitation and Sense terminals.
IND780 Installation Manual
WARNING!
Load Cell Input Resistance (ohms)
Number of Load Cells
24 Gauge 20 Gauge
(meters/feet)
243/800 610/2000
60/200 182/600
30/100 91/300
16 Gauge
(meters/feet)
1219/4000
304/1000
152/500
2-27