5-18 Parameter setting
IM 12B6B3-E-H
5-3-1. Parameter specific functions
Code 1 pH/ORP Choose the main measuring parameter. The option of the ORP input is used with
an inert metal electrode as measuring sensor which gives a reading directly in
millivolts. This signal can then be interpreted to give information about the
oxidation state of the process solution, and derived information like the absence
of a compound (like Cyanide for example which is destroyed in oxidizing
solutions).
Code 2 PRM.2 Enable the use of a second measuring parameter simultaneously with pH (the
main parameter).
With the correct sensor (e.g. FU20), ORP measurement is possible as parameter 2.
With the same sensor, rH measurement is possible as parameter 2, this is
calculated from pH and ORP and is a value which gives the oxidizing power of
the solution while compensating for the effect of pH.
This function is particularly useful for applications where both the pH and
oxidation-reduction potential of the process need to be controlled. The availability
of both measurements in a single system is much more convenient, (and more
economical) than two separate systems.
Note that in both cases a suitable sensor combination is needed to make this
possible. The Yokogawa FU20 (4-in-1) sensor can be used for this purpose, or a
combination of individual sensors. Contact your local Yokogawa sales office for
advice regarding applications and sensor selection.
Code 3 & 4 Z1.CHK & The EXA PH402 has an impedance check capable of monitoring the impedance
Z2.CHK of all sorts of sensor systems. In order to "fine tune" this diagnostic tool it is nec-
essary to set it up to match the sensors used. The default settings give a good
setup for a conventional system comprising pH glass sensor and a
reference electrode, either as individual electrodes or as a combination style
sensor. The impedance limits will need to be adjusted to get the best from
systems using heavy duty, or fast response electrodes.
The impedance measuring system has a very wide span requirement. As it can
measure in kΩ and also in GΩ (10
9
) there are hardware switches to set high
range (1MΩ to 2 GΩ) or low range (1kΩ to 1MΩ) measuring. As a default the
system is set to measure high impedances on input 1 (the one normally used for
the pH glass sensor input) and low impedances on input 2 (the one normally
used for the reference input). Examples of where these settings need to be
changed from the default, are Pfaudler enamel sensors which need two high
impedance settings, and Platinum sensors with a standard reference, which need
two low impedance settings.
In applications that have a tendency to leave deposits on the electrodes, and to
clog the reference sensor junction there is the possibility to use the impedance
check on the reference sensor to initiate the wash cleaning process. This
provides an excellent way of handling variable processes and intermittent batch
operations.
The temperature compensation of the impedance measurement is for conven-
tional pH glass sensors. When other sensors are used, switch this feature off.
Code 5 CAL.CK The calibration checking feature, when enabled, gives security against entering
wrong calibration data. For example when aged sensors are due for
replacement, the EXA flags an error message and prevents a calibration being
completed where the subsequent measurement can only exhibit errors and drift.
Limits are set for the maximum permissible Asymmetry potential, and Slope.
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