(2) If a sign “----“ on top of display and measuring value are shown in turn, it suggests
that CALIB knob has reached a mechanical boundary; nevertheless, if a sign “----“ on
bottom of display and measuring value are shown in turn, it suggests that SLOPE
knob has reached a mechanical boundary. If it shows " " on display, it
suggests that both CALIB and SLOPE have reached their mechanical boundary. It is
available for user to turn the knob in a reverse way if abovementioned conditions
occur. If it still fails to reach a desired calibration value, it means that a shift to
zero-point potential or slope is way much. It is recommended to use new pH standard
buffers or conduct maintenance for pH electrodes. Replace the pH electrode if above
two methods fail.
5.2 Inspection of ORP electrode:
ORP electrodes require ORP standard buffers to check & adjust its relative potential.
1.
Switch to ORP measurement mode.
2.
Press to enter calibration mode. It shows current measuring value and STDBY sign
with mV sign twinkling on display. At the moment, relay is turned off, analog output will
remain what it was prior to HOLD status and start calibration.
3.
Rinse the electrode with distilled water, place it into a known ORP standard buffer and
adjust CALIB knob until it reaches a correct ORP value.
4.
Open the backboard of the unit and install a jumper between GLASS and REF terminals to
have them short-circuited. Turn the CALIB knob until it shows 0mV and then remove the
jumper.
°
C 9891 standard buffer at 25
°
C, 220mV±5%
10
245mV
20
228mV
25
220mV
30
212mV
40
195mV
50
178mV
60
160mV
70
142mV
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