HF scientific MicroTOL Online Turbidimeter old series- 0-1000 NTU - Manual (Page 21)

MICRO TOL (12/04)
Rev. 2.7 15
6.0 Instrument Offset
In certain instances, you may wish to use an offset factor to calibrate your instrument
rather than performing a physical calibration of the instrument (as described in section
5.2). This procedure is not recommended in lieu of regular instrument calibration but it
can be used in situations where the number of instruments used makes regular calibration
prohibitive. This calibration technique will make the instrument accurate only at
turbidity levels in the immediate vicinity of the grab sample and not in the full range of
the instrument. Note that the key icon will be illuminated whenever an offset used. The
maximum offset is ± 1.00 NTU. If instrument variation is greater than 1 NTU a full
calibration is recommended.
The procedures are as follows:
1. Collect a grab sample of the process water that is being monitored by the instrument
and record the turbidity reported by the instrument.
2. Take the grab sample and measure its turbidity using your laboratory turbidimeter
(contact the HF scientific, inc. customer services department for examples of
laboratory turbidimeters).
3. Compare the turbidity reported by the instrument to that obtained in your laboratory.
If the readings are very close, then no offset adjustment or calibration is required and
you may stop the procedure at this step. However, if the readings are substantially
different (but less that 1 NTU), you may continue on in this procedure to utilize the
offset option to improve the turbidity reading of the instrument so that it will agree
with your laboratory reading between calibrations.
4. Select the calibration-offset function of the instrument by pressing the MODE/EXIT
button until the OFFSET and the arrow beside CAL are illuminated on the display.
Refer to the following screen.
5. At this point, the lower row of the display will indicate the operational status of the
offset function (ON or OFF). You may change this status by using the
t and u
buttons. Once you have set the desired operational status of the offset function press
the
↵
button to accept it. If you turned the option off, you can return to AUTO mode
by pressing MODE/EXIT.
6. If you turned the option ON, you will be prompted to enter the offset required. This
will add or subtract the value of the offset to the measured NTU value. As an example
if the Micro TOL measures the process at 0.16 NTU but the laboratory instrument
read the sample at 0.12 NTU, adding an offset of –0.04 would result in the Micro
TOL displaying 0.12 NTU.