Scale does not return to zero or reads wrong under load — the scale must float
Symptom
The empty scale does not return to zero, the zero creeps between batches, or the scale reads right empty but wrong under load.
Likely causes
- Hardened cement in the inlet sock (bellows) from the screw.
- A stiff or kinked air hose to the discharge valve or vibrator.
- A water pipe connected without a flexible section.
- Build-up between the hopper and the frame, or a stone jammed beside it.
- A stay rod adjusted too tight, or a safety chain carrying weight.
- A ladder, grating, cable tray or tool resting on the hopper; ice in winter.
Most likely and cheapest to check first.
Checks
- Finger test: with the scale empty, press gently down on the hopper rim and let go. The reading must return to exactly the same zero. Then press up.
- Walk round the scale and look at every point where something touches the hopper.
- Squeeze each sock by hand. It must be soft, with no cement packed inside.
- Check that safety chains hang slack and stay rods have their design clearance.
Fix
- Free the scale before changing any setting.
- Clean or replace hard socks with soft, flexible ones; tighten their clamps.
- Give every hose and pipe a loop or flexible section.
- Remove build-up and anything resting on the hopper.
- Verify the scale with test weights after any mechanical change.
Parts you may need
The golden rule
A scale only weighs what hangs freely on its load cells. Anything that touches the hopper and also touches the frame steals or adds weight. This is the cause of most “electronic” weighing faults. Check that the hopper floats before you touch the controller.
COST OF NEGLECTA sock that has gone hard with cement can hold back several kilograms on a cement scale. The scale reads correctly at zero, then wrong under load, and nobody sees it on the screen.
FIELD TIPOn a mix with 300 kg of cement per m³, a scale reading 2 % low puts 6 kg less cement in every m³. On 50,000 m³ a year, that is 300 t of cement missing.
FIELD TIPA sensible internal routine: zero every shift, check with a reference weight weekly, verify selected points every 3 months and calibrate fully every 6 months. On two- or three-shift plants, shorten the calendar intervals.
⚠ Every check inside a machine starts with full lockout. Safety disclaimer