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CH250 ORP/pH Digital Controller
- Product Details
- Specifications
- Installation
- Operation
Sanitiser and pH, Controlled Automatically
The CHEMTROL® CH250 keeps your pool or spa water balanced around the clock. It measures both the sanitiser level (as ORP) and the pH, and switches your chemical feeders on and off as needed — clear, safe water without daily manual dosing.
Proven in pools around the world for more than 30 years, the CH250 is the set-and-forget choice for residential pools, commercial pools and spas, hotels, health clubs and apartment buildings. Every setting is on the front panel, and the electronics carry a 5-year warranty.
ORP (oxidation-reduction potential) is a measure of how actively the sanitiser is working, so the CH250 works with all the common sanitisers — chlorine, bromine and other oxidisers.
Key Features
- Controls sanitiser and pH from one unit, each with its own set-point and alarms
- Works with chlorine, bromine and other common sanitisers
- Doses acid or alkali for pH — set once to suit your sanitiser
- Safety interlock stops dosing if the pH goes out of range
- Proportional feed eases off as each reading nears its set-point, so small pools and spas are not overdosed
- Separate overfeed safety timers stop a feeder and raise the alarm if dosing runs too long
- High and low alarms you can see and hear, plus a remote alarm output
- Every setting clearly labelled on the front panel, and kept through power failures
- Rain- and splash-proof cabinet with clear window cover, and a 5-year electronics warranty
CH250 Specifications
| Item | CH250 |
|---|---|
| Controls | Sanitiser (measured as ORP) and pH |
| Sanitiser set-point | ORP 250 to 950 mV (factory setting 700 mV) |
| pH set-point | 4.5 to 9.5 (factory setting 7.5) |
| Display range | ORP 0 to 999 mV; pH 0 to 14 |
| Accuracy | ORP ±5 mV; pH ±0.1 |
| Readouts | Digital LED readouts, ORP (3 digits) and pH (2 digits); indicator lights for feed mode, feed status and alarms |
| ORP sensor | Platinum electrode with 3 m cable; no calibration needed |
| pH sensor | Glass electrode with 3 m cable |
| Feed modes | Off, manual or automatic; on/off or proportional feed |
| pH feed | Acid or base, selectable |
| Outputs | Sanitiser feed and pH feed, each 5 A at supply voltage |
| 4–20 mA output | Optional |
| Alarms | High and low out-of-range alarms and overfeed alarms; audible, visual and remote (powered or dry contact) |
| Safety | Separate overfeed safety timers, sanitiser/pH interlock, diagnostic self-test, safety flow switch input; settings kept through power failures |
| Plumbing | PVC tees for 1/2", 1-1/2" or 2" line; bypass line assembly available |
| Cabinet | Polystyrene, rain- and splash-proof, with clear window cover, 22 x 18 x 10 cm |
| Electrical | 230 VAC or 24 VAC (please specify when ordering); draws 0.25 A, excluding feeders |
| Warranty | 5 years on the electronic module; 1 year on other parts |
Need a hand choosing sensors, plumbing or dosing pumps? Call us on 1300 585 820.
CH250 Installation
Installing the CH250 takes three steps: power, sensors and chemical feeders.
Controller
Mount the controller on a wall in a secure spot, out of direct sun and away from stored chemicals, at least 3 m from the water’s edge and within about 3 m of the sensors (they come with 3 m cables; 8 m and 16 m extensions are available). Wire it to the pump timer, in parallel with the circulation pump, so it can only dose while water is flowing. A qualified electrician should make the connection, following local wiring rules.
Sensors
Fit the ORP and pH sensors after the pump and filter, away from elbows and other turbulence. On a 1-1/2″ or 2″ line they can sit in the main line in PVC tees; on larger lines, mount them on a 1/2″ bypass line. Our bypass line assembly includes a strainer, flowmeter, safety flow switch, isolating valves and a sampling tap — with a bypass line, the safety flow switch is essential, so no chemical is fed if the line is shut or blocked. Tighten the sensor fittings by hand only, never with a wrench.
Chemical Feeders
Connect the sanitiser and the acid (or alkali) dosing pumps to the controller’s two outputs, and inject the chemicals downstream of the sensors and of the filter and heater. For a bromine or chlorine erosion feeder, fit a corrosion-resistant solenoid valve on the feeder’s intake line.
Bypass Line Assembly for ORP and pH Control
CH250 Operation
Once set up, the CH250 runs itself. Every function is labelled on the front panel, and the two readouts show the ORP and pH at a glance.
Factory Set-points
The ORP set-point comes set at 700 mV, the level recommended to kill germs and bacteria and keep the water in good condition. ORP also responds to pH, stabiliser (cyanuric acid) and the overall water quality, so test the sanitiser regularly and fine-tune the set-point if needed.
The pH set-point comes set at 7.5. At 7.5 the water is comfortable for swimmers and the chlorine works well. Below 7.4 it causes eye irritation and corrosion of equipment; above 7.6 it also irritates eyes, and leads to cloudy water, scale, stains and weaker sanitiser.
These are factory defaults, not fixed values: the operator can change them at any time to suit the water and local health requirements.
Changing a Setting
Press SETPOINT, then ORP or pH — the display flashes. Use the up and down arrows to reach the value you want, then press SETPOINT again to save it. The alarm limits, the safety timers and the pH calibration are changed the same way, with their own buttons. To choose a feed mode, press ORP or pH until the Off, Manual or Auto light comes on.
When first switched on, the controller shows its set-up menu: acid or base feed for pH (acid is the default, for liquid or granular chlorine; base is for trichlor tablets), the sanitiser/pH interlock, and the safety flow switch. Press both arrow buttons together to see it again at any time.
Alarms and the Safety Timers
Each reading has high and low alarm limits (from the factory, 650 to 900 mV for ORP and 7.0 to 8.0 for pH). If the ORP is low, the red alarm light flashes and sanitiser feed carries on so the water can recover. If the pH goes out of range, the alarm flashes and dosing stops until it is put right — chlorine works poorly at the wrong pH. This sanitiser/pH interlock can be switched off in the set-up menu.
The overfeed safety timers guard against an empty drum, a failed pump or a blocked line. They are factory set at 15 minutes for sanitiser and 5 minutes for pH, normally plenty to reach the set-point. If a feeder runs longer, the controller stops it, turns on the alarm and flashes the overfeed time. Once the cause is fixed, switch the feed mode to Off and back to Auto to reset the timer.
Back to Factory Settings
Your settings are kept in memory, even through a power failure. To return a set-point and calibration to the factory values, hold the ORP or pH button for 5 seconds.
