Mettler Toledo IND780 Guide D'installation page 50

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.
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:
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.
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.
2-26
METTLER TOLEDO IND780 Installation Guide
When installing Analog Load Cell boards, to prevent electromagnetic interference twist the
connector wires before attaching the connector to the board.
TSR =
Table 2-7: Recommended Maximum Cable Lengths
TSR (Ohms)
350
87 (4-350 Ω cells)
43 (8-350 Ω cells)
Load Cell Input Resistance (ohms)
Number of Load Cells
24 Gauge 20 Gauge
(meters/feet) (meters/feet)
243/800 610/2000
60/200 182/600
30/100 91/300
Figure 2-41: Load Cell Connections
16 Gauge
(meters/feet)
1219/4000
304/1000
152/500
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