AWE Direct

AWE Instruments

P7685 pH controller for proportional dosing, pH correction and control. With 2 x PFM, PWM or On / Off Control Relays and expandable 4-20mA output.


The P7685 pH controller for proportional dosing is available in either panel mounting or surface mounting configuration.

Model number P7685-W is supplied in a surface mounting enclosure

Model number P7685 pH controller is supplied in panel mounting configuration.

P7685 pH Controller For Proportional Dosing Introduction

The P7685 pH controller is designed to provide reliable, accurate, repeatable and dependable measurement and control of many industrial process. For those applications where precise control is required our model P7685 pH controller is the ideal partner featuring two proportional outputs, an expandable 4-20mA output and an alarm relay with delay timer.

With a 16 character alphanumeric LCD that displays the measured parameter and provides information about the state of the control and alarm relays. Also accessible is an indication of the operating condition of the sensor.

The versatility of the microprocessor accompanied by the user-friendly software allows the programming of the functions, routine checks and calibration to easily be accomplished even by untrained operators.

The model P7685 pH controller is a microprocessor panel mounting pH / mV & Temperature instrument. The controller is designed for control panel mounting in a 92 x 92 mm din standard cutout and is also available as surface mounting instrument. The unit operates from a power supply of either 110 VAC or 230 VAC 50/60Hz.

The model P7685 pH controller is able to measure and proportionally control pH or Redox (ORP) millivolt. The measuring discipline is user selectable and the pH input is also selectable for either Glass pH Probes or Antimony pH Probes.

The temperature input provides both a selectable temperature indication and auto temperature compensation of the pH range.

The P7685 controller is able to measure pH across the 0.00 - 14.00 pH scale, ±1000mV on the Redox (ORP) millivolt scale and from -10ºC - +110ºC on the temperature scale. The temperature measurement and Automatic Temperature Compensation are through the use of either a Pt100 temperature sensor. These are available from AWE Direct as either a pH Electrode with a built in Temperature Sensor, or as a separate stand alone temperature sensor.

When measuring pH we suggest pairing our instrumentation with an AWE pH electrode or another good quality electrode. For Redox measurement we recommend pairing the P7685 with an AWE Platinum band Redox Probe or another precision Redox probe. We also have a Antimony pH Probes for use with applications where Hydrofluoric Acid may be present. 

Proportional Control Relays, PFM, PWM, or On / Off Control and Alarm Relay.

The model P7685 pH controller features two control relays which can be programmed for either On/Off control, PFM control to proportionally control electronic metering pumps or PWM to time proportionally control solenoid valves or small pumps.

The P7685 is also fitted with an adjustable alarm relay with delay timer. This can operate on both a high and low measured value.

The P7685 proportional control relays offer PFM (pulse frequency modulation) output for proportional control of our electronic dosing pumps. The P7685 has adjustable set points and proportional band selectable for either one acid and one alkali-dosing pump.

In this instance the pH value of the measured solution can be efficiently corrected using either an acid dosing pump and an alkali dosing pump. For a pH value below the desired setpoint (e.g. a measured value of 6.00pH requiring correcting to a value of 7.00pH) the P7685 controller would call for the alkali metering pump to dose. When correcting from a value of 8.00pH to 7.00pH the P7685 controller would call for the acid dosing pump to dose.

The PFM output signal from the P7685 will mean that the a compatible dosing pump such as our ATAM series will automatically vary the frequency or number of strokes the pump makes per minute. As the pH scale is logarithmic the amount of chemical required to correct from a pH of 5.00 to 7.00 is ten times greater than the amount of chemical required to correct from 6.00 to 7.00 pH.

Using a proportional control pH controller like the P7685 means that when correcting from 5.00pH to 7.00pH the controller will call for the pump to dose at a much higher rate when initially correcting from 5.00 pH and as the measured value reaches 7.00 pH the controller will call for the pump to dose a small amount or less frequently to ensure that the required pH value is both reached precisely and the amount of correcting chemical being dosed is delivered as efficiently as possible. 

The P7685 pH controller for proportional dosing is also able to be setup for a duty and assist type installation. This is particularly useful in a number of applications specifically when a certain pH value has to be reached quickly or held during process control. For instance if a pH value of 2.00 pH has to be maintained during a process - the P7685 can operate two different pumps both dosing a strong acid. Normally one of these would be a dosing pump with a large output and the second being a small dosing pump. The larger of the pumps can be proportionally controlled to bring the pH down to a level close to 2.00 pH (approximately 2.50pH), then a second pump could be called to trim the pH to the desired level of 2.00 pH. Depending on the process and whether the pH value rises during the process - either the smaller pump or larger can be called to efficiently maintain the required pH value. (2.00 pH in this example.)  

pH controller with expandable 4-20mA for proportional control

The P7685 pH Controller 4-20mA proportional output is an industry standard current output signal which can be used with a number of compatible devices including PLC's, Data-loggers, and other associated items.

The P7685 pH Controller with an expandable 4-20mA output signal, means that the 4-20mA output can either represent the full 0 - 14.00 pH scale or a proportion of the range. So for instance the 4-20mA can be set over the 7.00 to 10.00 pH range where a 4mA is produced at 7.00 pH and a 20mA signal is produced at the 10.00 pH value. 

By incorporating an expandable 4-20mA signal the pH controller can work with an input device such as a dosing pump or another piece of control equipment. This could be used to proportionally control the pH value by either increasing the frequency or number of strokes the pump makes per minute to allow for precise control and efficient use of chemical.  

The isolated output corresponds to the measuring range selected which will expand in units of 1pH and can be programmed for either 0 - 20 mA or 4 - 20 mA.

The P7685 pH controller for proportional dosing in either panel mounting or surface mounting configuration with two control points on/off, PFM for proportional control of dosing pumps or PWM for proportional control solenoid valves, alarm relay with delay timer and isolated and expandable 0 (4) -20 mA current output has the electronics housed into an anodised aluminium case providing excellent EMC properties, and the rear of the case is fitted with two plug in connector blocks for ease of installation and maintenance.

P7685 pH Controller Specifications 

Input: Any AWE combination electrode or other good quality electrode.

Range pH: 0.00 - 14.00 pH.

Range Redox (ORP): 0 - ±1000mV

Display: 16 character alphanumeric LCD.

Temp Range: -10 - 110ºC or 14 - 230ºF

Automatic Temp Comp: Automatic via PT100 Sensor.

Manual Temp Comp: Manually Selectable from 0 - 100ºC 

Zero: Adjustable

Slope: Adjustable

Resolution: 0.01 pH.

Set Points: 2 on / off, high / low selectable, 5 amp non-inductive.

Action: On / Off, PFM (Pulse Frequency Modulation) or PWM (Pulse Width Modulation).

Hysteresis: ±10% adjustable.

Alarm Relay: 1

Action: Min or Max 0 - 60 mins after activation of S1 / 2.

Current Output: Expandable 0 - 20mA or 4 - 20 mA (programmable) isolated to 600 ohms.

Power supply: 230 - 115 volt at 50 / 60Hz.

Power Consumption: 5 VA

Weight: 850 grams panel mount version.

Dimensions: 96 x 96 x 155mm cutout 91.5 x 91.5mm

Ordering: Please Specify model:- P7685 Panel Mounting pH Controller and P7685-W Surface Mounting pH Controller

P7685 pH Controller Data Sheet

P7685 Data Sheet