Service manual

MDS E-SCAN MPR E-SCAN OPERATION/CALIBRATION
22
The final option of the calibration menu is “Anlg. 0" which activates the following display:
The analog zero adjustment is
used to correct for any shifts in
the measurement voltage. After
calibration and before
compensation, an analog zero
adjustment may be needed to
“zero in” the measurement
reading due to measurement
voltage shifts that could occur
when going from room
temperature to the process base
temperature used for the
temperature compensation run.
Analog zero adjustment may also
be needed after installation to
make instrument readings agree
with normal testing methods.
The measurement voltage displayed contains both analog zero and temperature compensation
adjustment. This is the voltage used to obtain an interpolated value from the calibration table
that will reflect an accurate displayed reading in Brix, Solids... (Range is 0-10 volts.)
The analog adjustment value ranges from 0 to 4095, with 2048 representing the zero voltage
point. Therefore, any value above 2048 results in a positive voltage adjustment and any value
below 2048 results in a negative voltage adjustment. The maximum manual adjustment allowed
in either the positive or negative direction is 1.5 volts, so there are 614 counts for a 1.5 volt span
or 41 counts for a .1 volt shift. The remainder of the resolution beyond +/- 1.5 volts is used for
temperature compensation.
Auto Adjustment
To perform automatic analog zero adjustment, the current measurement reading should be
recorded in the E-Scan when the sample is taken from the process. This can be accomplished in
normal mode of operation using the +/- button on the front panel. An “S” character is displayed
on the normal mode screen to indicate that the sampled reading has been recorded. The sampled
reading can also be recorded via the analog zero adjustment screen shown above.
The final part of automatic adjustment consists of entering the lab reading of the sample taken.
Using the previously recorded sampled reading and the lab reading, the software will
automatically determine the amount of analog offset needed to “zero” the instrument. The newly
calculated analog zero value is displayed as a digital number in the range of 1434-2662.
Analog Zero Adjustment Screen