03-09-05 23
given sensor measurement range the only valid scale factor figure is given in the
table Analog current scale factor for SLS
It is NOT CORRECT and will lead to erroneous results if the measurement range
is simply divided by the current range!!
If an absolute distance between the target and the sensor (or some other ref. Point)
is to be computed, it is necessary to be aware of the fact that the fixed calibration
point between the sensor and the current output is defined at the Stand-Off
distance as being 10 mA for a 0-20 mA sensor and 12 mA for a 4-20 mA sensor.
Referencing of analog current output to sensor - target distance
4 - 20 mA case
Compute distance D (sensor - target): D = (12 - I) * SF
I
+ SO
Where:
SO = Stand-Off distance i.e. distance from sensor front to MR
midpoint
SF
I
= Analog current output scale factor. Expressed as ”mm/mA”.
I = Analog current output in mA.
D = Measured distance from sensor front to target in mm.
Example: Sensor is SLS5200/300 => SF
I
= 12,8 mm/mA SO = 300 mm
D = (12 - 5,5) * 12,8 + 300 = 383,2 mm
4 12 20 I (mA)
D (mm)
Far End
Stand-off (SO)
Close End
SO is ”fixed point” for the
relation between MR and I
SO (=300mm)
D
I = 5,5 mA
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