The FX-1000p is an amperometric chlorine analyzer, which means that the chlorine residual reading is determined by reading the electronic amperage of the measuring cell. The amperage level is directly proportional to the level of free chlorine available in the sample stream. In the case of reading total chlorine, the unit is actually reading converted free iodine from the potassium iodide that is added to the cell for total chlorine readings.

The cell itself is constructed such that the sample runs through it, does so at a continuous and fixed rate. Any additional flow is allowed to overflow to waste from a drain below the overflow weir. The sample stream runs down through the lower block, where it mixes with vinegar (and potassium iodide where total chlorine is being analyzed), and then flows upward through the measuring cell. Within the cell, the vinegar provides pH buffering to a value of 4.0, and aids in keeping the cell clean. If potassium iodide is being used to read total chlorine, it chemically converts any free and combined chlorine residuals into free iodine, which is then read as a total chlorine reading. The cell utilizes a mixer and 150 PVC balls to ensure even chemical mix, clean probes, and consistent readings. Very pure grade of gold and copper are used in the construction of the probes to ensure accuracy. Sample flow leaves the cell from the top, and runs out a secondary drain to waste.

The cell probes are connected to the amplifier section of the electronics, where the low-level amperage is boosted and ranged to a useable signal. The output of the isolation amplifier is then doubled, which is used in the final 3 output stages of the circuit. These are the LED Display, the alarm circuit, and the 4-20 milliamp DC output signal.