Aquametrix AM-TBR Turbidimeter User Manual - Manual (Page 21)

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6. 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 Water Analytics 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 and 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.