Metrohm 767 Calibrated Reference - Manual (Page 11)

3 Procedure for checking instruments
767 Calibrated Reference Instructions for Use
7
3.2.1 U/mV, pH
carry out on instrument or sen-
sor:
carry out on Calibrated
Reference:
compare display
with:
remarks
1. screw off cable at sensor (for plug-in
head electrodes, otherwise use
corresponding accessory cable, see
chap. 5.2
close cover place sensor in
storage tube
2. connect sensor cable to
socket (5)
3. measure mV mV value (5)
4. open cover mV value (5) compare with
permitted toler-
ance; note value
5. connect sensor cable to
socket (4) permitted variation
from value noted
under step 4:
±0.1 mV (short-
time larger devia-
tions are normal)
6. connect sensor cable to
socket (6) mV value (6) observe polarity;
(switch measuring
range if required);
compare with
permitted tolerance
7. measure pH close cover pH value (6) set U
as
to pH 7 if
necessary
8. open cover pH value (6) compare with
permitted tolerance
End of check
Steps 9...12 are of secondary importance. In general it is sufficient to carry out this check once per year.
For instruments with earthed circuits (e.g. all Titrinos and early series of 692/713) or for instruments without an earth socket (604,
704, 744) these steps are not relevant. Further Information to steps 9...12 can be found in chapter 2.5.
9. measure mV connect sensor cable to
socket (5) note display as
under step 4
10. additionally connect cable
6.2150.020 (from accesso-
ries in case) to socket (6)
11. insert banana plug of cable in step
10 in earth socket of tested instru-
ment. Banana plug of shielding re-
mains open.
do not touch sockets (4),
(5), (6) during the meas-
urement
observe display
while connecting
the cable
permitted variation:
±0.1 mV display as
under step 5
(short-time larger
deviations are
normal)
12. remove cable from step 11 remove cable from
socket (6)
If the variation of the measured values is too large then first exchange
the original sensor cable against the reference cable in the accessories.
When the check is finished recalibrate the electrodes.