Sensor Characteristics
Correct adjustment and calibration of the overall system are crucial for precise and reliable measurements.
For load cells, the simple ratio of the bridge voltage UBridge to the measured supply voltage USense in mV/V is often not sufficient. Here the measured value must still be converted into a weight specification. To convert a measured value into a load, sensor-specific characteristic values must be specified. The information can either be taken from the data sheet or test report of the sensor or determined by calibrating the entire system (see chapter Sensor calibration).
The unit of the result is determined by the nominal load. If the nominal load is specified in kilograms, for example, the result is also output in kilograms.
The weight is calculated using the following formula
Sensitivity
The nominal characteristic value of a strain gauge sensor describes the sensitivity, i.e. how much the output signal changes under a certain mechanical load, and is usually specified in mV/V.
Object 0x80n0:23 in the sensor-specific RMB areas (n = 3 (Ch. 1), n = 7 (Ch. 2)) can be used to parameterize the nominal characteristic value of the connected sensor. The value can be taken from the information on the sensor data sheet or even more accurate from the test report supplied. Alternatively, it can be determined by calibrating the entire system (see chapter Sensor calibration).
Zero Balance
The zero offset denotes the output value of the sensor in the unloaded state in mV/V. An ideal sensor shows an output signal of zero at zero load. The real deviation is specified in the sensor's test log and entered in the object 0x80n0:25 in the sensor-specific RMB ranges (n = 3 (Ch. 1), n = 7 (Ch. 2)) or can be determined by calibrating the overall system (see chapter Sensor calibration).
Nominal Load
The nominal load describes the maximum load that the strain gauge sensor can measure without being damaged or losing accuracy.
This information can be found in the sensor's data sheet and is entered in object 0x80n0:24 in the sensor-specific RMB ranges (n = 3 (Ch. 1), n = 7 (Ch. 2)). The firmware always calculates without units, the unit (kg, g, lb) used here must then also be applied to the result
Gravity of Earth
The force of gravity can influence the measurement, especially if the strain gauge sensor is used for weight measuring. The default value of the earth's gravitational force is 9.80665 m/s², but this value can vary depending on the geographical location and should be taken into account for precise measurements. This value can be changed channel-specifically in object 0x80n0:26 in the sensor-specific RMB ranges (n = 3 (Ch. 1), n = 7 (Ch. 2)).
Scale factor
The scaling factor can be used to rescale the process data value into another unit. To change the display from kg to g, for example, the factor 1000 can be entered in object 0x80n0:27 in the sensor-specific RMB ranges (n = 3 (Ch. 1), n = 7 (Ch. 2)).
Reference load
The reference load (also known as "adjustment weight") is a known load that is used to manually calibrate the strain gauge sensor. If the reference load is specified in object 0x80n0:28 in the sensor-specific RMB ranges (n = 3 (Ch. 1), n = 7 (Ch. 2)), the gain can be set when calibrating the overall system (see Sensor calibration). The reference load must be within the measuring range of the sensor and should be at least 20% of the nominal load.