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## What the Tonnage Monitor Measures
A servo press tonnage monitor measures the actual forming force during each stroke using strain gauges mounted on the press frame or slide. The reading tells you:
- Whether the die is working correctly
- Whether material thickness is consistent
- Whether a double blank has entered the die
- Whether a punch has broken
## Reading the Display
Most tonnage monitors show:
- **Peak tonnage:** maximum force during the stroke (in tons or kN)
- **Tonnage curve:** force vs. position graph for the full stroke
- **High/low limits:** alarm thresholds
## Setting Limits Correctly
**High limit:** Set at 110-115% of nominal tonnage. This catches:
- Double blanks (two sheets entered die)
- Die crash (foreign object in die)
- Incorrect material (wrong thickness or grade)
**Low limit:** Set at 80-85% of nominal tonnage. This catches:
- Missing blank (no material in die)
- Broken punch (punch not forming)
- Incorrect material (too thin)
## Interpreting Tonnage Curves
**Normal curve:** Smooth rise to peak at BDC, then rapid drop on return.
**Double peak:** Two force peaks in one stroke — indicates progressive die with two forming stations, or a problem with die timing.
**Early peak:** Force peaks before BDC — punch hitting material too early, check die setup and material thickness.
**Gradual increase over time:** Die wear or material hardness increasing. Schedule die maintenance.
## Calibration
Calibrate tonnage monitor annually using a reference load cell. Accuracy should be within +/-2% of full scale.