Load Cell & Scale Signal Calculator

1 · Expected Load Cell Output

The #1 scale check: is the cell putting out the signal it should? Compare this to your meter.

920i exc 10 V Hardy exc 5 V 3 mV/V 2 mV/V

Excitation (V)

Rated output (mV/V)

Cell capacity

Applied load

Units label

Expected output @ load

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Full-scale output

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Reverse: measured signal (mV) → implied load

Implied load

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Output (mV) = Excitation × mV/V × Load ÷ Capacity. Healthy cells read ~0 at no load, climb linearly, and never exceed full-scale output. A signal above full-scale — or one that won't return to ~0 at no load — is a dead giveaway of a bad cell.

2 · System Capacity (summing box)

Multiple cells under a vessel. The empty vessel (dead load) eats part of your capacity.

# of load cells

Capacity per cell

Dead load (empty vessel)

Total system capacity

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Net usable (live)

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Dead load uses

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Rated capacity per cell

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Watch dead load — a heavy vessel on undersized cells wastes resolution.

3 · Display Resolution

Capacity (full scale)

Display divisions (counts)

Weight per division

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Divisions = capacity ÷ increment. Keep it to what the system can actually resolve.

4 · Bridge Resistance Quick Reference

Disconnect the cell and ohm it out. Off-spec or low isolation = suspect cell.

Check	350 Ω cell	1000 Ω cell
Input (EXC+ ↔ EXC−)	~350–415 Ω	~1000–1100 Ω
Output (SIG+ ↔ SIG−)	~350 Ω	~1000 Ω
Any lead ↔ cell body	> 1000 MΩ (megger) — low = moisture/damage

Confirm exact values on the cell's spec sheet. Off-spec, or any reading to ground = failing cell.

5 · Load Cell Wiring Colors (Rice Lake)

Colors vary by maker AND model — always confirm against the cell's wiring guide. The two most common Rice Lake patterns:

Wire	Pattern A RL20000 / 30000 / 35023 / 75016 / 90000…	Pattern B PC / RC / SB series, RLSB2, RLMK15, RLC…
+ Excitation	Green	Red
− Excitation	Black	Black
+ Signal	White	Green
− Signal	Red	White
+ Sense (6-wire)	Blue *	Brown *
− Sense (6-wire)	Brown *	Yellow *
Shield	Bare / Orange	Yellow

* Sense leads vary most by model (also seen Orange/Blue, Green/Grey). Colors are NOT universal across brands — when unsure, ohm it out and check the model's wiring sheet.

6 · Hardy C2 Load Cell Wiring

Hardy's standard C2 color code (HI 3000 / 4050 / 6200 / 6500 C2 load points). Non-C2 cells vary — check the supplier.

Wire	Color
+ Excitation (EXC+)	Red
− Excitation (EXC−)	Black
+ Signal (SIG+)	Green
− Signal (SIG−)	White
C2 + (data)	Grey
C2 − (data)	Violet
Shield	Ground / bare

C2+ (grey) & C2− (violet) are Hardy's electronic-calibration data lines — they let the module read the cell's capacity/output for C2 cal (no test weights) and per-cell diagnostics (Integrated Technician).

Some Hardy series use an "East Coast" code instead: +EXC Green, −EXC Black, +SIG White, −SIG Red (C2 still grey/violet). A standard C2 cable is these six wires plus shield — if a cell has extra wires, they're sense leads that tie to the excitation connections.

7 · Rice Lake 720i / 920i Connector (J1)

Load cell terminal pinout on the A/D card — land each wire (by its color, above) on the right pin.

Pin	Function
J1-1	+ Signal (SIG+)
J1-2	− Signal (SIG−)
J1-3	+ Sense (SENSE+)
J1-4	− Sense (SENSE−)
J1-5	+ Excitation (EXC+)
J1-6	− Excitation (EXC−)

6-wire cable: remove jumpers JP1 & JP2 first. 4-wire: leave JP1 & JP2 on. (Dual-channel J2 uses JP3 & JP4.)

8 · Summing Box / Junction Box

Ties multiple load cells into one home-run cable to the indicator. Each cell lands on its own channel — same wire colors as above.

Hardy HI 6020IT / JB: up to 4 cells per box (8 with two boxes). The IT version reads each cell's voltage & weight individually — isolate a bad cell in seconds. Trim-pot version handles non-C2 cells. Rice Lake 4-channel: 4 cells, a trim pot per channel for corner balance.

Troubleshooting: uneven corner readings = a cell needs trim or is failing. On Hardy IT, switch to the internal test circuit to find the bad one.