While the theory of monitoring conductivity is simple, in practice it can be very frustrating. While simple 2 electrode sensors are inexpensive and can provide accurate data, continuous monitoring of even relatively clean water can foul the electrodes and degrade the measurement. Maintaining accuracy is made more difficult when the amount of solids dissolved in the process varies over a wide concentration range. In this case, a simple 2 electrode sensor is limited by its cell constant, which means it cannot measure the process accurately.

The Q45C4 4 electrode conductivity monitor is the answer for monitoring almost any water based process. Drinking water, plating bath solutions, cooling water, process wash water or virtually any other aqueous system can be monitored accurately and reliably. The unique drive/control scheme used in the 4 electrode system allows a single sensor configuration to be used in conductivity ranges from 0-200 uS to as high as 0-2,000 mS (0-2.5). The "auto-ranging" feature enables the monitor to display the actual conductivity value during "overshoot" conditions. For chemical making applications, a concentration display can be selected for a limited number of acids and bases. If your application involves very low conductivity/resistivity measurement, ATI can provide the Q45C2 system that is used in process waters with conductivities below 20 uS.

Benefits of a 4 Electrode Sensor - Q45C Conductivity monitors are designed to use a rugged 4 electrode sensor that provides wide range conductivity measurement without the need for multiple sensors. Virtually all conductivity applications ranging from 0-200 uS up to 0-2,000,000 uS (0-2.5) can be reliably measured using this unique and flexible system. What can be accomplished with a single 4 electrode sensor with increasing cell constants. The "one sensor fits all" approach to conductivity measurement eliminates the need to inventory multiple sensor types, as well as the confusion in matching cell constants to conductivity ranges.

The 4 electrode sensors not only provide wide range measurement capability, but also excellent resistance to electrode coatings that can degrade measurement accuracy. Changes in electrode condition are compensated for in the electronic transmitter, so even partially fouled sensors continue to produce accurate measurements. And should the sensor become so fouled that it requires cleaning, the monitor will display a "fouled sensor" indication to ensure that operating personnel are alerted.

Sensors for the Q45C4 system are available in a variety of mounting configurations: convertible system with 1" NPT threads for pipe or tank mounting, 1 ½" or 2" sanitary style fittings in 316SS and insertion style for 1 ¼" NPT hot tap assemblies that allow the sensor to be removed from service without shutting down the process.

How a 4 Electrode Sensor Works - In a traditional 2 electrode sensor, each electrode performs two functions. First, the electrodes are used to generate a "drive potential" through the aqueous solution. Second, the electrodes are used to measure the level of current flow as the conductivity of the solution varies. It is this dual role that limits a 2 electrode sensor to a narrow functional conductivity range.

A 4 electrode sensor splits the two functions between two set of electrodes. One set of electrodes is used to generate the drive potential through the aqueous solution. The other set of electrodes is used to measure the current that flows between the two drive electrodes. Because these two functions are separate, the 4 electrode sensor does not suffer the polarization effects that limit a 2 electrode sensor to a narrow functional range. This allows a single 4 electrode sensor to operate reliably over the entire 0-2.5/cm conductivity range.

Monitor Features

Loop-powered, AC or Battery Versions: This line of microprocessor based instrumentation allows for easy implementation of loop-powered or battery-powered capability within the same instrument. This instrument can be rapidly converted between any of these versions with no requirements for software change.

• Loop-powered (16-35 VDC) Transmitter, 4-20 mA output
• Line-powered (115/230 VAC) Analyzer, dual relays, dual 4-20 mA outputs
• Battery-powered (9 VDC) Monitor/Data Logger, dual 0-2.5 VDC outputs

Portable Data Logger: For even greater versatility, a portable unit powered by a standard 9V battery is also available. The dual 0-25 VDC outputs are assignable to conductivity and temperature. This instrument can be supplied with an internal data logger, making it ideal for short term monitoring at remote sites. The unit will run for 10 days on a single battery and the data logger will store up to 32,000 data points

Intuitive User Interface: Four button programming provides intuitive navigation through the menu driven user interface.

Dual Alarm Relays/Analog Outputs: AC operated systems provide two relays that are configurable for either "control mode" or "alarm mode" of operation.

Flexible Calibration: Two point and sample calibration options include stability monitors to check temperature and main parameter stability before accepting data.

Diagnostic Messaging: Diagnostic messages provide a clear description of system condition, which eliminates confusing error codes that are difficult to decipher.

Sensor Features

4 Electrode Style Sensor: Allows the sensor to be used over 0 to 2,000,000 uS range.

PEEK Sensor Construction: Electrode holders made of PEEK, a high performance thermoplastic that provides outstanding mechanical strength and chemical resistance. High structural integrity ensures accurate conductivity measurement.

Multiple Mounting Styles: Sensors available in 1" NPT convertible style, insertion style and 1 ½" or 2" sanitary styles.

Titanium Electrodes: The four electrodes used in the sensor are made of titanium for greater chemical resistance.

Sensor Diagnostics: Sensor diagnostics are used to alarm the user in the event of loss of sensor seal integrity or integral temperature sensor failure. Automatic foulant rejection circuitry is used to compensate for the effects of sensor fouling. As the two drive electrodes become coated by the process solution, a feedback mechanism involving the two sensing electrodes detects the decrease in drive potential and automatically reestablishes the proper drive potential. When the degree of coating reaches a limit where compensation is no longer possible, the diagnostics actuate and alarm to signal that the sensor requires cleaning.

Multiple Sealing Materials: Multiple sealing materials are used to preserve sensor integrity over a wide range of chemical processes and varying temperature.

Specifications - Monitor

Measuring Range	0.0 to 200.0 to 2,000 uS; 0.00 to 20.00, 0.0 to 200.0 to 2,000 mS
Repeatability	±3% or span or 0.1 uS whichever is greater
Sensitivity	0.05% of span or 0.1 uS whichever is greater
Non-Linearity	0.3% of span or 0.1 uS whichever is greater
Response Time	6 seconds to 90% of step input at lowest setting
Display	Large 4 digit main display, 0.75" characters, 12 digit alpha numeric second line display
Power	16-35 VDC for loop powered units, 115/230 VAC, 50/60 Hz, 10 VA Max, 9 VDC for battery power
Control Relays	Two SPDT relays, 6A @ 250 VAC, 5A @ 24 VDC, resistive
Relay Mode	Programmable for control or alarm function
Analog Outputs	Isolated 4-20 mA, 550 ohm max load. Two assignable 4-20 mA outputs, 550 ohm max.
Data Logger	Battery version only, stores 32,000 data points
Temperature	-20 to 60°C
Humidity	0-95% RH, non-condensing
Weight	2 wire or battery unit: 1 pound Other configurations: 1.5 pounds
Enclosure	NEMA 4X (IP-66) polycarbonate wall, panel or pipe mount

Specifications - Sensors

Measuring Range	0 to 2,000,000 uS
Wetted Materials	PEEK, titanium, Viton, EDPM, 316 SS with sanitary or insertion body styles
Sensor Cable	6 conductor plus 2 shields, HDPE jacket
Response Time	90% in 2 seconds
Temperature Compensation	Pt1000 RTD
Temperature Limits	-10 to125°C
Pressure Limits	0-100 psig
Max Sensor to Analyzer Distance	60 feet
Sensor Body Option	1" NPT convertible 1 ¼" insertion 1 1/2" or 2" sanitary

Ordering Information

Other configurations available For pricing, please call AFC International at 1-800-952-3293, 219-987-6825 or fax 219-987-6826 or email sales@afcintl.com

Description	Catalog No.
Q45C4 Resistivity/Conductivity Monitor, 24VDC, 2 Wire, 0.05 Cell, Titanium, ½" NPT Compression Fitting, 15' Cable	Q45C4-1-1-1
Q45C4 Resistivity/Conductivity Monitor, 115 VAC with 2 Relays & 2 Outputs, 0.05 Cell Titanium ½" NPT Compression Fitting, 15' Cable	Q45C4-2-1-1
Q45C4 Resistivity/Conductivity Monitor, 24 VDC, 2 Wire, 1.0 Cell, 316SS, ½" NPT SS Compression Fitting, 15' Cable	Q45C4-1-2-1
Q45C4 Resistivity/Conductivity Monitor, 115 VAC with 2 Relays and 2 Outputs, 1.0 Cell, 316 SS ½" NPT SS Compression Fitting, 15' Cable	Q45C4-2-2-1
Q45C4 Resistivity/Conductivity Monitor, 24 VDC, 2 Wire, 0.50 Cell, 316 SS 1 ½" Sanitary Fitting, 15' Cable	Q45C4-1-5-1
Q45C4 Resistivity/Conductivity Monitor, 115 VAC with 2 Relays and 2 Outputs, 0.5 Cell 316 SS, 1 ½" Sanitary Fitting, 15' Cable	Q45C4-2-5-1

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Q45C4 Conductivity Monitor