Calibrating a Grain Cart Scale on an M640 (Custom Code)
Grain cart scales on a Weigh-Tronix M640 use the custom calibration method (not standard). Most indicators from Central City Scale arrive already calibrated — usually a final adjustment is all you need. Custom calibration corrects the scale by a ratio: you weigh a load, note what the M640 shows, then compare it to what it actually weighed on a certified scale (the elevator).
1. Set the CONFIG number
Under the CONFIG menu, the number is read digit by digit:
First two digits: always 98 for grain carts.
Third digit — display increment: 3 = 10 lb, 4 = 20 lb, 5 = 50 lb update. Your choice.
Fourth digit — printer: set to 9 if you use a printer (harmless to leave in if you don't).
Last digit: always 0.
Common grain cart CONFIG numbers: 98300, 98390, 98400, 98490, 98500, 98590.
2. Pick your starting custom number
CCS grain cart systems are dual-bar systems. Which starting number you use depends on how the system is wired — check the junction box:
3-bar with resistor (junction box has external 5-pin plugs): start at 37500
3-bar, no resistor (wires hard-wired into the junction box): start at 27775
5-bar Weigh-Tronix (never uses a resistor, CONFIG 98590): start at 45000
3. Work out the new custom number
Formula: (actual weight ÷ displayed weight) × last custom number.
Example: certified scale read 58,654 lb (actual); the cart showed 59,240 lb (displayed); current custom is 37,500. 58,654 ÷ 59,240 = 0.9901; 0.9901 × 37,500 = 37,129 = your new custom number.
4. Enter the new calibration
Press and hold Hold/Menu for three beeps — display shows SET.PAS.
Using RM (raises the digit) and Hold/Menu (shifts to the next digit), enter 640, then press Print/Select.
Press Print/Select again — display reads CONFIG. Press Hold/Menu — display reads CUSTOM.
Press Print/Select — the last custom number appears (note it for the formula).
Enter your new custom number with RM and Hold/Menu, then press Print/Select (display reads CUSTOM).
Press G/N to reach 640, then G/N again to return to weighing. Calibration is saved.
Checking it: the best check is to stand on the hitch while the cart is hitched to the tractor — it won't read accurately on the jack stand. The custom number is a starting point, not a constant; it settles to within about 1% as you dial it in, so a few passes may be worth it.
Questions, or want us to check your calibration? Call Central City Scale at 800-582-3175.