Valeport 803 - 10 Appendix 4 - Calibration

Valeport Ltd © 2019
0803805i - Model 803 ECM
Page 24
10. Appendix 4 - Calibration
The calibration certificates for the X and Y channels are provided separately from this manual together with
the instrument’s warranty certificate. The calibration certificates also include the serial numbers of the
electronics unit and sensor. Calibrations are normally carried at the 2 Hz output rate, and at speeds up to 1
M/sec, and linear extrapolation is used above that speed [the sensors have a linear characteristic at higher
speeds].
The calibration function of the EM sensor has 3 elements to it:
Hydrodynamic Calibration
This is the “shape” of the calibration curve and is a function of the type and size of sensor. The equation used
is based on normalised output of zero counts at zero speed and a standard number of counts per metre/sec
[usually 1000]. The hydrodynamic calibration takes the form of a number of straight line fits and the number
of lines used and the slope, offset and break point for each line is shown on the calibration sheet. The same
calibration is used for +ve and –ve flow.
Zero Offset
This is the number of counts [output before calibration conversion output] at zero flow, and is particular to a
sensor, sensor axis and electronics. The zero counts are shown on the calibration sheet.
Gain Factor
This is the factor by which the sensors counts per metre/sec must be multiplied to normalise it to the
standard counts/metre per second [e.g. 1000 counts/metre/sec]. The gain factor is particular to a sensor,
sensor axis and electronics and is shown on the calibration sheet.
The complete calibration function takes off the Zero Offset from the raw data count, multiples the result by
the Gain Factor and then calculates the flow from the Hydrodynamic Calibration.
Users can read the calibration factors by sending the following control codes [after interrupting the unit]:
#172 Reads the X channel Zero Offset in counts
#173 Reads the Y channel Zero Offset in counts
#176 Reads the X channel Gain Factor
#177 Reads the Y channel Gain Factor
#190 Reads the X channel Hydrodynamic Calibration
#191 Reads the Y channel Hydrodynamic Calibration
The calibration factors can be changed, but users should fully understand what they are doing before doing
this.
Calibrations should be carried out with the unit in NOCAL mode, in which no calibration calculations are
carried out and the unit outputs raw data counts. To move in to or out of this mode:
#007 NOCAL
Sets the unit into NOCAL mode [raw counts output]
#007 CAL
Sets the unit into CAL mode [Speed output]
and
#030
Reads if unit is set in CAL or NOCAL mode