Current Threshold Calibration
It is the process of setting the trigger level of current-sensing shutdown above the real operating current and below the stall current. If the threshold is too low the motion is cut mid-travel; if it is too high the mechanical end stop is strained for longer than necessary. The practical approach is to measure the current at the heaviest normal load and leave roughly 20–40% margin on top.
During calibration there are two values you need to measure: the current at the most strained moment of normal operation and the current reached when it stalls against the end point. The threshold is placed between these two values, closer to the normal current.
- Temperature effect: cold grease and frozen mechanics raise the current on the first movement in the morning. If you set the threshold in summer conditions, you will get early triggering in winter.
- Ageing: bearing wear and dirt build-up increase the operating current over time; re-measuring the current periodically explains most early-triggering complaints.
- Ramp effect: the starting surge rises to typically 5–8 times nominal. To avoid counting this surge as the threshold, the driver applies a short blanking period at start-up; extending the ramp time makes the job easier by reducing the surge to 2–4 times.
On the PT500 this setting is made with the A1 and A2 pots. Adjust both directions separately, testing with the real load.
Context where this term is used: DC Motor Driver Selection Guide