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P a g e
5.1.5
Load Cell Parameters
The SP-010 provides 3 Sensor Parameters which may be updated based on the specific load cell being used.
The Load Cell sensors maps to Sensor 0 of the SP-010. The SP-010 Load Cell Sensor Parameter base address is 0x08c0
(Modbus 0xf460). All values are 32-bit float values.
Parameter
Offset
Name
Range
Factory
Default
Description
0
0x00
Sensitivity
0.1 to 100
1.0
Sensitivity in mV/V
1
0x10
Range
1 to 100000
1000
Specified full scale range
2
0x20
Impedance
0 to 15000
0
Setting to 0 allows auto measurement
2
0x30
TARE
+/- 100000
0
Write ‘actual’ value (ie: 0 to Tare)
5.1.5.1
Sensitivity
The Load Cell sensitivity is typically given as a mV/V ratio and indicates the expected signal generated per applied
bridge excitation voltage when a the rated load is applied. For example, a load cell with a sensitivity of 10 mV/V and a
rated Range of 1000 kg will generate 10 mV if 1 volt is applied to the bridge excitation signals with a load of 1000 kg.
5.1.5.2
Range
The Load Cell range is specified in kg, lbs, or other weigh units of measurement. The SP-010 assumes all weights are
provided in kilogram (kg). When entering the full-scale range, it is recommended that the value is converted to kg. An
alternative is to change the
units of measure
, enter appropriate scale factors and set the lock bit in the sensor
descriptor field.
Typical load cells also specify a maximum ‘overload’ value. The SP-010 will set the maximum
measurement value to 150% of the specified range.
5.1.5.3
Impedance
The Load Cell impedance is specified in ohms. If this value is set to 0 the device will measure the attached load cell on
the next power or device.
5.1.5.4
TARE
When a value is written to the TARE register an adjustment factor is calculated and stored for subsequent
measurements. It is typically used to ‘zero out’ weights associated with tote boxes and other discrepancies in a
weighing system.
T
factor
= T
value
– R
raw
R
final
= R
raw
+ T
factor
Where:
T
value
is specified TARE value
R
raw
is the unadjusted reading
R
final
is the final, adjusted reading
For example, if the current reading is 1.2 and the TARE value is 0.0, the internal adjustment value will be set to -1.2
The TARE adjustment is made after the User Calibration scaling. Writing to the TARE value during User Calibration is
ignored. SP-010-1 units that offer DIO signals may be configured to allow an external digital signal to ‘trigger’ a TARE
function.