Fine-Tuning The Indicating Accuracy - Bosch ETT 008.31 Repair Instructions

6.3

Fine-tuning the indicating accuracy

In devices for which calibration is compulsory by law, the calibration seal on the rear wall of the device must be removed for fine-tuning.
To do so, loosen the screw beneath the seal and swivel the safety panel to the side (function switch S 60 is now accessible).
The gas outlet must lead to the open air and have a sufficiently wide cross section. If the required hose length exceeds 2 m, the hose
diameter must be increased. Neither pressure nor vacuum must be allowed to form in the hose.
Particularly during fine-tuning, the zero-gas inlet must be able to take in perfectly clean outside air. In case of doubt, bring outside air
in from a suitable atmosphere using a hose.
Test-gas connection
The test gases which are required one after the other for the purpose of fine-tuning must be connected up to the calibration-gas inlet.
Set an admission pressure of approx. 0.7 bar at the bottle-pressure reducer. At this pressure, the flow resistance of the integrated non-
return valve is overcome and a suitable flow rate achieved (up to 4 l/min). If a flow meter is connected to the gas outlet, the flow can
be adjusted (to a minimum of 0.5 l/min).
Correct sequence for fine-tuning
The following order of procedure must be complied with:
Measuring channel
1. HC measuring channel,
small measuring range
2. CO measuring channel,
small measuring range
3. CO measuring channel
2
4. HC measuring channel,
large measuring range
5. CO measuring channel,
large measuring range
Within a measuring range,
proceed as follows (using the example of No. 1 HC channel, small measuring range, engine-speed LED does not light up):
a) Fine-tuning the upper-range value
Set function switch S 60 to position 2 (upper-range values). Select the HC channel using the "Select" button, and simultaneously
press "Enter o" to switch on the fine-tuning function.
°C display window:
HC display window:
Engine-speed window: The calibration factor accepted during the last fine-tuning is displayed.
Introduce a flow of test gas no. 5 into the device via the calibration-gas inlet.
Change the calibration factor indicated in the engine-speed display window with the "ENTER o" or "TEST u" buttons in such a
way that the value currently displayed in the HC window exactly matches the certified test-gas value (this value is displayed with
a certain delay after the calibration factor is changed).
! Do not press any buttons!
Introduce a flow of mean-value gas (test gas no. 4) into the analyzer and check that the display deviates from the test-gas value
by less than 2%. In this case, the mean value does not have to be adjusted.
If the display differs from the test-gas value by more than 2%, the mean value must be re-calibrated as described in b) below.
In all cases, now press the "Select" button. The calibration factor of the upper-range value is now accepted and the next possible
function displayed.
26
Fine-tuning
Upper-range value
Mean value
Upper-range value
Mean value
Upper-range value
Mean value
Upper-range value
Mean value
Upper-range value
Mean value
E. Ei E. Ei E. Ei E. Ei (set upper-range value) E. Ei
Current measured value
with test gas
Nr. 5, 3.800 ppm C H
3 8
Nr. 4, 2.000 ppm C H
3 8
Nr. 6, 1% CO
Nr. 1, 14% CO
2
Nr. 4, 7.5 % CO
2
Nr. 2, 16.000 ppm C H
3 8
Nr. 6, 8.000 ppm C H
3 8
Nr. 3, 9% CO
Nr. 4, 5% CO