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Rated Output
This specifies the output in millivolts per volt (of excitation) calibrated at full load. Most cells have 2mv/v but some have 3mv/v outputs.
Excitation Voltage
This specifies the recommended supply voltage to the load cell. This varies from 10 to 20 volts depending on the load cell type. Within limits, the higher the supply voltage, the higher the output of the load cell will be. However, load cell accuracies are quoted for a particular test voltage (usually 10 volts) and any variation from this either up or down can impair the performance of the ioad cell. Too high a supply voltage can cause undesirabie heating effects within the gauges and can iead to damage
Zero Balance
This specifies the maximum output tolerance at no load condition and is normally 1% of nominal zero output.
lnput Resistance
This specifies the resistance between the two input terminals and usually varies between 350 and 1000 ohm.
Output Resistance
This specifies the resistance between the two output terminals and usually varies between 350 and 1000 ohm.
Note: The rated output combined with the output resistance determines the output current of the load cell. When load cells are connected in parallel, it is this current which should be matched as closely as possible from one cell to another to facilitate time consuming corner corrections in the field.
Insulation Resistance
This specifies the minimum insulation resistance between the wiring and the load cell body. This should be greater than 5000 Megohm.
Maximum Safe Load
This specifies the maximum load which can be applied to the load cell without damaging it.
Maximum Load Ultimate
This specifies the maximum load which can be applied to the load cell without breaking it.
Note: if a load cell is loaded between safe overload and ultimate overload permanent damage can occur. One easy way to check this is to measure the zero balance. lf this is out of specification then the load cell has been permanentiy damaged.
Compensated Temperature Range
This specifies the temperature range within which the load cell will be within tolerance. This is normally -10 to +40°C (1R60).
Operating Temperature Range
This specifies the temperature range within which the load cell will still operate although some specifications willbe out of tolerance.
Combined Error
This is defined as the algebraic sum of non-linearity and hysteresis.
Non-linearity Error
This is defined as the deviation of the increasing load cell calibration curve from a straight line.
Hysteresis Error
This is defined as the difference between load cell output readings for the same applied load, one reading obtained by increasing the load from minimum dead load and the other by decreasing the load from maximum capacity.
Repeatability Error
This is defined as the difference between load cell output readings taken from consecutive tests under identical loading and environmental conditions.
Temperature Effect on minimum dead Load output
This is defined as the change in minimum dead load output due to change in ambient temperature and is given as a % of rated capacity.
Temperature Effect on sensitivity
This is defined as the change in sensitivity due to a change in ambient temperature and is given as a % of rated load.
Minimum Dead Load Output Return
This is defined as the difference in load cell output at minimum dead load, measured before and after full load application.
Creep
This is defined as the change in load cell output occurring with time whilst under constant full load and with all environmental conditions and other variabies remaining constant.
Note: R60 specifies particuiar time parameters to be used when measuring both creep and minimum dead load output return.
Load Cell Accurancy
This is a very misunderstood term and in the past it has been treated differently in different countries. For this reason the 0IML (Organization internationale de Métroiogie Légale) has written a ‘recommendation” outlining how load cells should be defined and tested. This international Recommendation No 60 (IR60) is used by leading Weights and Measures Authorities around the world as their basic guideline when testing load cells and as a result load cell accuracy specifications are now clearly defined.
C1 ---- 1000 scale intervals
C2 ----2000 scale intervals
C3 ---- 3000 scale intervals
C4 ---- 4000 scale intervals
C6 ---- 6000 scale intervals
The maximum permissibie error always has to be within the envelope for the complete weighing system. When the ioad celi is tested in isolation then only 7O% of the total system error is allowed according to IR60