Ref :UM-CT7-11-001 Issue : 01 Date : 28/04/2011 Page 31 of 35 8 Maitenance 8.1 Calibration We recommend calibrating CT7 after transport and when it is exposed to important temperature change. CT7 is designed as instrument not requiring calibration. Nevertheless, we recommend to calibrate is after delivery and when instrument is subjected to important temperature change . Usually calibration is performed when one suspects any pollution or if time elapsed since the last calibration is estimated too long, or if some measured values are suspect. Place CT7 at the calibration target, activate Menu MEASURE / Calibrate. Cal Temp 28.5 C Note:
OPO has devised a VW jig allowing direct absolute calibration of a gauge just before using it. This is the only procedure that allows checking the calibration of the instrument and correcting it if needed. Note: The short term calibration is not requested because the instrument uses a digital lock in detection by which the ratio of reflected signal to the source signal is directly recorded. By doing this, the main reason for instrument drift is suppressed: that is the source intensity variations. The remaining drift cause is the cleanliness of the collimator and collecting lenses. But these are inside a cavity and further protected by stops so that pollution has little chance to get there.
That is why the instrument can remain stable for years without recalibration like an electronic multi‐meter. But of course accidental pollution by smoke for instance can happen, and after several years, it would be more secure to check the calibration. The great difference with other instruments is that you really do not need frequent (daily) recalibration. These anyhow rely on a gauge that can change over a period of time. 8.2 Battery Charge CT7 uses two NiMh 2450mAh AA cells as a source of energy. Any USB socket of a PC is able to provide current up to 500mA. Hence, full charging of empty CT7 accumulators having a capacity of 2450mAh may last 5 to 6 hours .
The internal CT7 fuse (resettable) provides protection of the power source. The state of charge can be checked thanks to STATUS option: v3 is battery voltage. When V3=2.2V, the batteries are empty, at 2.9V they are fully charged. If the CT7 is ON while charging the charge time increase considerably (2..3 x). For battery change the instrument shall be dismounted. We advice to change the batteries each 2 years during periodic revision at OPO. This document is OPO property. It may not be either used or copied without authorization. OPO sprl, Crawhez 9, 4890 Thimister Clermont, Belgium. +32 87688989 - +32 87598990