Calibration
Page 19
© 2016 Valeport Ltd
6. Calibration
Selecting
DIRECT EM COMMS
at the OPTIONS MENU enables the user, using a PC in terminal mode
via the optional DC data lead to read and alter the EM calibration.
Connect the unit to a PC via the data interface lead supplied. Connection details are given in
Section 4.6.3.
Run a terminal emulation program on the PC, ensuring that communications are correctly set to
4800 baud, 8 data bits, 1 stop bit, no parity bits, flow control NONE.
The EM calibration has 3 parts to it:
HYDRO CAL
This is the “shape” of the calibration curve and for normal routine
calibrations the same calibration is used for all units of the same
type.
SYSTEM GAIN FACTOR
The Gain Factor is specific to a combination of sensor and CDU, and
is the factor by which all raw data from the electronics are multiplied
to normalise the data to a standard counts per metre/sec.
SYSTEM ZERO OFFSET
The Zero Offset is specific to a combination of sensor and CDU, and
the number of counts which the unit outputs at zero flow. See
section 6.1 below for details on re-setting zero offset.
Having connected up the CDU and PC and entered DIRECT EM COMMS, the unit will output EM
data at a rate of 2 Hz. Calibrated data from the EM electronics is in mm/sec. To communicate to
the unit and interrupt it, press and hold the “#” key on the PC. When the unit responds with a §,
enter a single # and press <cr>. The unit will respond with a “«” [this may not be visible in all
terminal programs if the font is not available] and then await a command. These commands are
a series of “#” codes
Code
Followed By space and
Operation
#007
Output_Format<cr>
Sets the output format of the unit to CAL or NOCAL.
CAL is data in calibrated units, NOCAL is raw counts
and is used for calibrating purposes
#030
Nothing<cr>
Reads the output format CAL or NOCAL
#028
Nothing<cr>
Sets the unit into run mode. Data is outputted at the
2Hz rate.
#170
Zero_offset<cr>
Sets the zero offset in counts
#172
Nothing<cr>
Reads the zero offset which has been set
#174
Gain_Factor<cr>
Sets the GAIN_FACTOR
#176
Nothing<cr>
Reads the GAIN_FACTOR which has been set
#190
Nothing<cr>
Reads the Hydro Calibration which has been set
#192
Calibration<cr>
Sets the Hydro Calibration
If the user wishes to alter the calibration from the factory setting, it is necessary to enter the
calibration coefficients. The calibration coefficients are stored within the micro-controller in an
ASCII text string. The format of this string depends on the type of calibration (line fit or polynomial
fit). The first part of the string will be the calibration function number, selected from the table
