Load Cell System Resistance; Din, Panel-Mount And Harsh Enclosures - Mettler Toledo IND131 Guia De Instalacion

The DIN, panel-mount and harsh enclosures are designed to accept a single load cell cable. This
cable attaches to the 7-position terminal block as shown in Figure 2-30 and Figure 2-31.
The J-box enclosure is designed to accept from 2 to 4 load cell cables into the housing and
terminate to a summing board inside the enclosure. A short cable from the summing board then
connects to the 7-position terminal block on the terminal. Both termination methods are described
in this section.
2.4.2.1.

Load Cell System Resistance

The IND131/331 terminals are designed to power up to four 350-ohm load cells (or a minimum
resistance of approximately 87 ohms). This equates to eleven 1000-ohm load cells. 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 terminal has a resistance greater
than 87 ohms before connecting the load cells. If the resistance is less than 87 ohms, the terminal
will not operate properly.
In addition, the maximum cable distance must be reviewed. Table 2-3 provides recommended
maximum cable lengths based on TSR and cable gauge.
2.4.2.2.

DIN, Panel-mount and Harsh Enclosures

Figure 2-33 shows the terminal definitions on the analog load cell terminal strip. 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.
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TSR =
For US AC models, systems including up to 8 load cells can be metrologically approved.
For non-US AC models, systems including up to 4 load cells can be approved.
Table 2-3: Recommended Maximum Cable Lengths
TSR (Ohms)
(meters/feet)
350
87 (4-350 Ω cells)
43 (8-350 Ω cells)
METTLER TOLEDO IND131/IND131x/IND331/IND331xx Installation Manual
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 90/100
16 Gauge
(meters/feet)
1219/4000
304/1000
150/500
2-21