HF scientific MicroTOL Online Turbidimeter - Manual (Page 20)

MICRO TOL (5/10) 14
Rev. 4.8
6.0 Instrument Offset
In certain instances, it may be desirable to use an offset factor to calibrate the 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 OFFSET 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 a laboratory turbidimeter
(contact the HF scientific customer services department for examples of laboratory
turbidimeters).
3. Compare the turbidity reported by the instrument to that obtained in the laboratory. If
the readings are very close, then no offset adjustment or calibration is required and the
procedure may be stopped at this step. However, if the readings are substantially
different (but less that 1 NTU), continue on in this procedure to utilize the offset
option to improve the turbidity reading of the instrument so that it will agree with the
laboratory reading between calibrations.
4. Select the offset function of the instrument by pressing the MODE/EXIT button until
the arrow beside CONFIG is illuminated on the display. Refer to the following screen.
5. Push the
↵
button until OFST is displayed on the lower row.
6. At this point, the lower row of the display will indicate the operational status of the
offset function (On or OFF). Change this status by using the
t and u
buttons.
Once the desired operational status of the offset function has been set, press the
↵
button to accept it. If the option was turned off, return to AUTO mode by pressing
MODE/EXIT.