The first and most core category consists of comprehensive performance indicators, covering five key parameters.
The first indicator is rated load, commonly referred to as measuring range, for which the designed measuring range value of the sensor must be specified. This value shall envelop the full load range under all normal operating conditions.
The second indicator is overload requirements. Overload is classified into two tiers: safe overload and ultimate overload. It must be emphasized that overload conditions should be avoided as much as possible during practical operation.
- Safe overload: It refers to the condition where the load borne by the sensor exceeds its rated load. After load removal, the measurement accuracy is only slightly compromised, yet a certain zero-point shift will generally occur. Our products feature a safe overload capacity of 200% to 300% of the rated load.
- Ultimate overload: When the load reaches this threshold, the sensor retains structural integrity; however, full load removal will lead to degraded measurement accuracy and substantial zero-point drift. Our products deliver an ultimate overload capacity ranging from 300% to 500% of the rated load.
When designing the rated load and overload parameters, customers are advised to comprehensively evaluate the reducer’s rated output torque, start-stop torque, and maximum instantaneous torque. In general, the rated load (measuring range) of a torque sensor must cover the output torque under normal operation. Ideally, the maximum measured load during regular operation accounts for approximately 70% of the full measuring range; the safe overload rating shall cover the maximum instantaneous torque that may occur in practice. On this basis, excessively raising the rated load is not recommended, as it will sacrifice the sensor’s signal-to-noise ratio.
The third indicator is precision, specifically repeatability precision — the deviation margin of readings when the same load is measured repeatedly. Our standard products control this metric within 0.3% F.S. (Full Scale).
The fourth indicator is accuracy, a term often confused with precision. Accuracy denotes the degree of deviation between measured values and true values, primarily affected by non-linearity and hysteresis. The combined accuracy of our products is maintained within 1% F.S.
The fifth indicator is eccentric load resistance, which describes the sensor’s performance when subjected to loads other than torque. Under such circumstances, the sensor must maintain high rigidity and minimal deformation, while spurious output (crosstalk) shall be kept as low as possible. This indicator shall be determined according to the sensor’s actual application scenarios:
- For cup-type reducers: The sensor can be coupled via cross roller bearings, which bear combined axial and radial forces as well as bending moments from the load end. As a result, only torque acts on the sensor during operation. This design suppresses crosstalk interference from extraneous loads to torque measurements, guarantees measurement accuracy, and significantly boosts system rigidity, so stringent eccentric load resistance requirements for the sensor are unnecessary.
- For hat-type reducers: They support flexible installation with either flexible wheel output or rigid wheel output. Regardless of the output configuration, the sensor is typically mounted with its outer ring connected to the reducer and inner ring linked to the load. All loads including bending moments generated by the load pass through the sensor, imposing strict requirements on its eccentric load resistance.
The above five indicators form the fundamental core of sensor design.
