IM 12B6C2-E-H
40
9. CHANGE FROM PH TO ORP MEASUREMENT
The PH200 transmitter can be used for pH
measurement and tor ORP measurement.
The factory delivers the instnument in the pH
configuration with the possibility to change
easily to ORP.
9-1. How to change pH measurement to
ORP measurement
Remove the cover after loosening the 4
screws. Now you have access to the elec-
tronics. Loosen the 4 screws that hold the
boards in place and remove them from the
enclosure. On the upper back-side of the
DlSPLAY-board there is a blue jumper
switch. Change the springjumper from the
upper contact to the lower contact and
make sure that the spring is in its locked
position to ensure good contact (see figure).
The PH200 transmitter can be reassembled
now, following the opposite sequence as de
scribed above. The next step is to reset the
memory of the transmitter. The following
simple procedure must be followed:
1. Push the key marked with *, push the NO
key 2 times till *SERV appears in the mes-
sage display, push YES.
2. The display shows *CODE 00; Change
the code 00 to 55 with the arrow keys.
Confirm selection with the ENT-key.
3. The display shows ERASE and now the
YES key must be pushed.
4. The display shows *SERV. Pushing the
MODE key finishes the procedure to
measure ORP.
9-2. Commissioning the transmitter
As ORP transmitter, the PH200 has basically
the same functions as explained earlier in
this manual. While commissioning, the
microprocessor will skip its relevant settings.
Instead of pH all values and limits are
expressed in mV.
9-3. Maintenance of the transmitter
Calibration of the ORP transmitter is a one
point calibration only. Although there are
several ORP buffers available, mostly the
unit is calibrated with grab sample, analysed
on the laboratory with reference method.
Automatic temperature compensation for
ORP is not possible, so the menus AUT.CAL
and TEMP are skipped during maintenance
menu after pushing the MODE key.
9-4. Special features
In many applications the ORP readings are
dependent on the pH of the process liquid.
In many applications we can eliminate this
influence by using a pH electrode as a refe-
rence electrode. Due to the high impedance
of the glass electrodes, the electrodes are
connected reverse, resulting in “ - “ readings
where nor mally “ + “ readings are expected.
This does not necessarily influence the ORP
control, since the output range is freely
selectable.
pH
ORP
