PCA340 Free & Total chlorine, pH & °C controller/analyser

The PCA family are process analysers for the continuous measurement of chlorine and temperature. Also, pH (PCA320, PCA330, PCA340) and ORP where specified. The analysers feature built in data logging, RS 485 digital output, dosing relays, and alarm relays packaged in a wall mount Nema 4 x enclosure. The PCA340 also features two analog outputs.

From drinking and wastewater treatment to pool and spa sanitation, monitoring chlorine levels has an important bearing on public health. It can also help with the running efficiency for heating system and industrial applications.

Chlorine, pH, ORP and Temperature analysers

The PCA300 family uses DPD Colorimetric method in which N, N-Diethyl-p-phenylenediamine indicator and a buffer are mixed together with the sample. The resulting chemical reaction causes a magenta colour to form in the presence of chlorine. The colour intensity is proportional to the concentration. The colour intensity is measured photometrically (light source at a specific wavelength and a photodetector) and converted to chlorine concentration, in mg/L, which is displayed on the front panel. The sampling interval for chlorine measurement is adjustable from 3 to 90 minutes.

The analysers have a dosing relay for the addition of chlorine by a dosing pump or chlorine generator when a reading is below the programmable set point. The technology used by this family for chlorine measurement is the same as that found in portable and benchtop colorimeters providing for consistent results when performing process verification with one of those types of meters.

The PCA320, 330 and 340 also utilise the HI-1005 amplified pH electrode with a built in pt100 temperature sensor and matching pin to measure both pH and temperature. The built in amplifier and matching pin provide for exceptional performance against any electrical noise generated by pumps and motors. These analysers have a programmable dosing relay for the adjustment of pH. The dosing relay can be activated by either on/off or proportional control.

The PCA340 features two selectable 0.20 or 4-20 mA signal output that are scalable for the transmission of readings to external recording devices. The analog outputs can also be set for dosing and used with dosing pumps that accept a 4-20mA analog input. The analog outputs can be used for any of the three measured parameters.

Through the system setup menu, users have the ability to enable or disable the low and high level of alarms for all parameters. The PCA family also offers overdosing protection that generates an alarm if something within the system is not working properly. The system will stop processes until the user corrects the error.

Backlit LCD Display

The PCA family has a backlit display that is easy to read from a distance and allows for up to three parameters to be displayed at a time.

Nema 4x protection

The analysers are enclosed in waterproof casing for superior protection against the elements. The front door of the case has a window for the measurement display while also shielding the DPD reagents from UV light to prevent premature degradation.

DPD Chlorine Measurement Method

The DPD colorimetric method is one of the most common and reliable methods to measure chlorine. The PCA family can use either free or total chlorine reagents and allow for 16,000 measurements to be performed.

Reagent Reminder

The PCA family has a reagent reminder feature to alert the user when the reagents are running low. When the reagents are changed, the counter is reset and the meter automatically tracks the number of readings performed.

Colorimeter Diagnostics

Advanced diagnostics allow for easy troubleshooting of the colorimeter. In the setup menu it is possible to select an option that allows the user to determine the difference between a dark read (LED off) and blank read (LED on). These analysers also automatically perform this check in order to determine when to alert the user that the sample cell needs to be cleaned.

Amplified pH/Temperature, probe (PCA320, PCA330 and PCA340)

An integrated pt100 temperature sensor allows for automatic temperature compensation of pH measurements and allows for monitoring temperature as well. The built in amplifier and matching pin provides for exceptional performance where other probes fail when placed in line with pumps and motors.

Data logging

The analysers can store up to 3500 readings (at least 7 days worth of records when set to a 3 minute sampling interval) that can be reviewed or downloaded to a Windows compatible PC using the HI-92500 software and the RS485 serial port. Logged records contain the date, time and reading of all parameters measured along with any alarm status.

GLP Data

The GLP data allows for the user to review the data and time for the last chlorine and pH calibration.

Digital RS485 output

The analysers have a RS485 digital output that allows for connection to a Windows compatible PC running the HI-925000 software. The software allows for remote monitoring, review of logged data, events and errors, and executing setup options.

Warning messages

Error messages are displayed when the reagents are expired or low and if the colorimeter cell needs to be cleaned.

Two analog outputs (PCA340)

The PCA340 features two selectable 0-20 or 4-20 mA signal output that are scalable for the transmission of readings to external recording devices. The analog outputs can also be set for dosing and used with dosing pumps that accept a 4-20 mA analog input. The analog outputs can be used for any of the three measured parameters.

Two dosing relays

The dosing relays of the analysers can be connected to a pH and/or chlorine dosing pumps. The chlorine relays are proportionally controlled, while the pH relay can be set for on/off or proportional control. The proportional control offers very fine control of doing to prevent any overshoot and wastage of chemicals.

Alarm relay

One SPDT alarm relay is provided that can be activated by adjustable upper and lower chlorine, pH and temperature limits.

Error relay

One SPDT error relay is provided and is activated when an error is present, including a problem with the colorimeter - such as when the reagent counter has reached zero, or when a reading is outside the range for a measured parameter.

Key features

• Backlit LCD Display
• Nema 4x protection
• DPD Chlorine measurement method
• Colorimeter diagnostics
• Reagent reminder
• Amplified pH/temperature probe
• Data logging of up to 3500 measurements
• GLP data for review of calibration information
• Digital RS485 output
• Two analog outputs for recording or dosing devices (PCA340)
• Two dosing relays
• SPDT alarm relay
• SPDT system error relay
• Warning messages
• Each PCA 300 series model is supplied with reagent bottles (2), reagent caps (2), 1 DPD compound powder, tubing and instructions

About chlorine

Chlorine is a strong oxidising agent that destroys mostly organic pollutants and bacteria and can combine with nitrogen containing compounds, forming chloramines. When dosing chlorine for disinfection, only a portion of the dosed chlorine remains active to actually continue the disinfection process.

When free chlorine combines with a nitrogen containing compound, it becomes a less efficient disinfectant called chloramines. The addition of these two parts gives total chlorine. The target is to keep free and total chlorine equal, and to maintain the combined chlorine concentration (chloramines) near zero. The presence of chloramines is not desired because of the distinctive ‘swimming pool’ smell caused by combined chlorines like di-chloramines. Beside this unpleasant odour, chloramines can irritate the eyes and the mucous membranes.

. . . . More about chlorine

Commercial chlorine for disinfection may be available as a gas (Cl₂), a liquid like sodium hypochlorite or bleach (NaOCl), or in a solid state like calcium hypochlorite, chloro-hydantoins or chloro-cyanuric acid compounds. These compounds, once dissolved in water, do establish equilibrium between the hypochlorous acid (HOCl) and the hypochlorite ions (OCl^-). Although both forms are considered free chlorine, it is the hypochlorous acid that provides the strongest disinfecting and oxidising characteristics of chlorine solutions.

The amount of hypochlorous acid in chlorinated water depends on the pH value of the solution. Changes in pH value will affect the HOCl equilibrium in relation to the hydrogen and hypochlorite ion. HOCl decreases and OCl^- increases as pH increases. At a low pH, almost all the free chlorine is in the molecular form HOCl and at a pH of around 7.5, the ratio between HOCl and OCl^- is 50:50.

Since the ionic form OCl^- is a slow acting sanitiser while the molecular HOCl is a fast acting, it is important to regularly measure the pH. As a general rule, a pH of about 7.2 is recommended to maintain fast acting disinfection conditions.

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