Checking Input Impedance Of A Ph Analyzer - Fig. 4.4; Operation As A Meter; Calibration For Ph Measurements - Fig. 5.1 - ABB 2410 Instruction Manual

...4 OPERATION AS A SIMULATOR
4.5 Checking Input Impedance of a
pH Analyzer – Fig. 4.4
All pH measuring instruments require an
extremely high input impedance (greater than
12
10 ) to operate corr ectly. If the input
impedance is degraded (due to contamination
of the connection block or connection cable)
the instrument may function correctly with a
low impedance signal, but gives incorrect
readings (low or high or, in some cases, off-
scale) when connected to an electrode pair.
The Model 2410 has the facility to check the
input impedance of the glass electrode using
the 1000M Ω position of the Function switch
and the reference electrode input using the
100K Ω position.
Refer to Fig. 4.4 and:
1 Set the Function switch to 'CALIBRATE'.
2 Set the Mode switch to 'pH'.
3 Set the Power switch to 'ON'.
4 Use the 'OUTPUT ADJUST' control to set
an appropriate pH value, e.g. 10 pH.
5 Set the Function switch to '1000M Ω'.
After an initial 'spike', the reading on the
pH analyzer under test should return to
within 0.1 pH of 10.00 pH. If the change in
the reading is greater than 0.1 pH the input
impedance is too low.
6 Repeat step 5 but setting the Function
switch to '100k Ω'.
For laboratory analyzers, the most likely
cause of the above is the coaxial input cable or
the BNC socket on the instrument under test.
For industrial systems, the cause is likely to
be attributed to:
the junction box in the electrode system
the wall mounting junction box
the interconnection cable
the instrument (less likely).

5 OPERATION AS A METER

5.1 Calibration for pH
Measurements – Fig. 5.1
For optimum measurement accuracy the
calibration procedure should be carried out at
frequent intervals.
Prepare 4 pH and 9 pH buffer solutions.
1 Connect the electrode to the BNC socket.
2 Set the Function switch to 'MEASURE'.
3 Set the Mode switch to 'pH'.
4 Set the 'TEMP °C' control to the
temperature of the buffer solutions.
5 Set the Power switch to 'ON'.
TEMP
C
40 60
25
20
0
CALIB
SLOPE
Temp mV pH
2
Fig. 4.4 Checking the Input Impedance
4
25
20
0
7
Temp mV pH
3
Fig. 5.1 Calibration for pH Measurement
OUTPUT
ADJUST
1000M
100k
80 CALIBRATE
MEASURE
100
TEMP
ON OFF
3
TEMP OUTPUT
C
ADJUST
1000M
40 60
100k
80 CALIBRATE
MEASURE
100
TEMP
CALIB
SLOPE
ON OFF
5
4
1
5
6
2
1
6
7