Emerson TCL instruction manual Model 499A CL-02 Sensor

MODEL TCL	SECTION 1
	DESCRIPTION AND SPECIFICATIONS

used to signal a fault condition. A fault alarm activates when an analyzer or sensor fault occurs.

When used for the determination of total chlorine, the Model 1056 analyzer is a single input instrument. The ana- lyzer is also available in a dual input version, where the second input can be pH, conductivity, dissolved oxygen, chlorine, or turbidity. For more information about the dual input option, refer to product data sheet PDS 71-1056.

MODEL 499A CL-02 SENSOR

The Model 499ACL-02 total chlorine sensor is used in the TCL sample conditioning system. Although the sensor is called a chlorine sensor, it really measures iodine. The iodine comes from the reaction between oxidants in the sample and the acetic acid/potassium iodide reagent added by the sample conditioning system.

The sensor consists of a gold cathode and a silver anode in an electrolyte solution. A silicone membrane, permeable to iodine, is stretched over the cathode. The analyzer applies a voltage to the cathode sufficiently negative to reduce all the iodine reaching it. Because the concentra-

tion of iodine in the sensor is always zero, a concentration gradient continuously forces iodine from the sample through the membrane into the sensor.

The reduction of iodine in the sensor generates a current directly proportional to the diffusion rate of iodine through the membrane, which is directly proportional to the concen- tration of iodine in the sample. Because the iodine concen- tration depends on the amount of total chlorine in the sample, the sensor current is ultimately proportional to the total chlorine concentration.

The permeability of the membrane to iodine is a function of temperature. A Pt100 RTD in the sensor measures the tem- perature, and the analyzer uses the temperature to compen- sate the total chlorine reading for changes in membrane permeability.

Sensor maintenance is fast and easy. Replacing the mem- brane requires no special tools or fixtures. Simply place the membrane assembly on the cathode and screw the retainer in place. Installing a new membrane and replenishing the electrolyte takes only a few minutes.

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