A pH analyzer is the instrument that turns acidity into something a control system can act on. It sits in the line or on the tank wall, reads continuously through a glass electrode, and holds a current output that a dosing pump, a controller or a recorder can follow. This range covers three panel-mount controllers built on the same electrode chemistry: a 4.3 inch flagship with two isolated outputs and a separate cleaning contact, and two 2.8 inch tiers that carry the same pH accuracy in smaller cases with a single output.
The tiers are easiest to read as a decision about the enclosure and the loop rather than about the measurement. All three read pH to ±0.02, and all three accept the same electrodes. What changes below the flagship is how many values the instrument can transmit at once, how many contacts it offers, and how much panel space it occupies.
What the controller measures
The primary measurement is pH. Behind it sits a second one, ORP, which the same instrument reads when an ORP electrode is fitted instead of a pH electrode. The two are not variants of each other: pH reports hydrogen ion activity on a logarithmic scale, while ORP reports the oxidising or reducing tendency of the solution in millivolts. A chlorinated stream can hold a steady pH while its ORP moves, so a disinfection loop and a neutralisation loop are measuring different things even when they sit on the same plant.
The flagship tier extends the pH span to -(2.0016.00) and supports an antimony electrode, which matters in strong acid and strong alkali where a glass membrane would not survive. The two smaller tiers work across 014 pH. On the ORP side the flagship reaches ±2000 mV, the economy tier is limited to -1000~+1000 mV, and the upgrade tier covers that span with ±2000 mV available to order.
How the measurement works
A glass measuring electrode and a reference electrode form an electrochemical cell, and the voltage across it depends on the hydrogen ion activity of the solution between them. The response is logarithmic, so a fixed change in millivolts corresponds to a fixed change in pH rather than a proportional one. The controller turns that voltage into a pH value using a calibration established against buffer solutions of known pH, and applies temperature compensation so that the electrode response is corrected to the temperature actually measured.
Three consequences follow, and all three matter more than the electronics. The first is that the measurement is a comparison, so the reference half of the cell is as important as the measuring half: a partly blocked or depleted reference junction appears as a reading that drifts or responds slowly, and no amount of recalibration cures it. The second is that the glass membrane is a consumable. It ages, it dehydrates if it is allowed to dry out, and it is attacked by hydrofluoric acid and by strong caustic at elevated temperature. The third is that temperature compensation corrects the electrode, not the process: where the pH of the process genuinely shifts with temperature, the compensation follows the electrode response and reports the true pH at that temperature, which is a different statement from the pH the specification was written against.
The compensation arrangement differs by tier. The flagship offers manual compensation plus automatic linear compensation, with dedicated acid, alkali and pure water compensation for the streams where a single linear model is not accurate enough. The upgrade tier accepts an NTC10K or Pt1000 sensor and the economy tier an NTC10K, both over a -10 to 130°C span. On every tier the usable span is set by whichever electrode is fitted, and the material supplies no temperature table for the electrode range.
Choosing between the three tiers
Start from the loop rather than the panel. If the installation has to transmit one value and switch one load, the smaller tiers do the whole job in a 96 x 96 mm or 100 x 100 mm cut-out. If pH and a second value both have to be transmitted, the flagship’s two isolated outputs are what make that possible without a second instrument, and its three contacts - two alarm and one cleaning - let a jet or brush cleaner be sequenced without borrowing an alarm relay.
Then check the supply, because the three tiers are not interchangeable there. The flagship accepts AC (85265) V or DC (21.626.4) V, so it will run on whatever a panel happens to provide. The economy tier takes AC 220 V ±10 % at 50 Hz or DC 24 V, and the upgrade tier AC 220 V ±10 % at 50 or 60 Hz or DC 24 V ±20 % with an input power of not less than 6 W. The material cautions expressly that these must not be mixed, and a panel supplied at a voltage outside the narrower ranges will need the flagship or a separate supply.
Then settle the panel itself. The three cases are different sizes and the front bezels are not interchangeable, so the cut-out has to be decided before the panel is made. Case material, gasket and ingress protection are not stated in the material, which matters on a washdown wall.
Selecting the electrode
The controller is only half the loop, and on most installations the electrode is what decides whether the measurement works. The material lists a partial range of matching electrodes - one plastic-body model for continuous online work and five glass models for general water quality - without a parameter table for any of them. Ranges, temperature limits, pressure limits and connection threads therefore have to be confirmed per model rather than read off this page.
Four questions decide the electrode, and they are worth answering before the instrument is ordered. What is in the medium: hydrofluoric acid, strong caustic, sulphides, oils, proteins and heavy solids each attack a different part of the cell. What temperature it runs at, including any cleaning or sterilisation cycle, since that drives both the electrode choice and how long it lasts. What the line pressure is and whether it varies, because the reference junction responds to pressure and a swinging or vacuum condition can pull the reference into the sample. And how the sensor will be reached: an electrode that cannot be withdrawn and cleaned without draining the line is an electrode that will drift.
The material’s own caution is worth repeating. The temperature compensation span is marked -10 to 130°C, but the usable measuring span belongs to the electrode, and no electrode temperature table is supplied. Where the process runs hot, that is a question for the quotation rather than an assumption from this page.
Outputs, alarms and the control loop
All three tiers provide an isolated current output, which keeps the instrument and the receiving device electrically separate and avoids a ground loop between them. The flagship has two channels, assignable across the measuring range, at ±0.1 %FS and meeting NAMUR NE43. The upgrade and economy tiers have one channel at ±0.2 %F.S. Every tier is rated for a maximum load of 750 Ω, which is high enough for a normal cable run but is not unlimited: the resistance of the cable and of the receiving instrument has to stay inside it, or the transmitted current can no longer be regulated and the value read at the far end drifts away from the value measured without any fault being indicated.
The alarm contacts are relay contacts, and the material states their switching capacity rather than their type alone. The flagship carries three SPST contacts, two for alarms and one for cleaning, in normally open and normally closed form, rated 250 VAC / 5 A. The other two tiers carry two contacts rated AC 250 V / 3 A. A dosing pump or a solenoid valve within those ratings can be switched directly; above them, or on an inductive load, the material’s own advice is to interpose a relay so that the instrument switches a coil rather than the load. That keeps the contacts inside their rating and moves the wear to a replaceable part.
Measurement limitations and selection considerations
The ±0.02 pH figure is the electrical accuracy of the controller. It is not the accuracy of the installed measurement, which is set by the electrode’s condition and age, by the freshness of the buffers it is calibrated against, by whether the compensation matches the actual stream, and by the medium itself. A coated bulb or a partly blocked reference junction moves the reading far more than the controller’s own error, which is why the routine that matters is cleaning, calibrating in fresh buffer, and replacing an electrode that will no longer pass rather than recalibrating one that has failed.
Several parameters are not stated anywhere in the material: the ingress protection rating, the ambient temperature and humidity limits, and the dielectric strength. Nothing here is inferred to fill those gaps. They are listed as information required, and the material’s own note that all figures are the supplier’s nominal values, to be confirmed against the delivered nameplate and manual, applies to the whole page.
Panel mounting also fixes an installation detail worth thinking about before the cut-out is made. The material illustrates a 15 degree angled electrode installation, which is a recommendation about how the sensor should sit so that its sensitive membrane contacts the medium fully and bubbles do not collect on it; it is not a second way of mounting the controller. The controller itself is a recessed panel instrument whose bezel sits at the panel face, and the material notes that where the artwork shows both arrangements the delivered manual governs.
Where a reading has to be taken to a sample rather than held in a line, the instrument is the wrong one: a pH meter is carried to the sample and read there, and it needs no supply, no wiring and no panel cut-out. The analyzer exists because the reading has to stay in place and drive something. Where the requirement is a single spot check, or a field survey across many points, the meter is both cheaper and more practical.
Ordering
A quotation can be issued from the duty described in the enquiry. The items that decide the answer are the medium and its temperature, the pH or ORP range expected and the band that has to be held, the line pressure and whether it varies, the mounting arrangement available at the measuring point and how much access there is for removal, how many values have to be transmitted and what will read them, whether the reading must drive dosing or only be recorded, the panel supply available, and the ingress protection the location calls for. Quantity, destination port and required delivery date complete it.
Every value below is taken from source documentation. Where a parameter is not stated in the available material it is marked as information required rather than estimated.
