SIGNUX CLA01

The SX-CLA01 measures free residual chlorine in treated water. Cell and electronics share one body, so the probe connects directly to an RS485 bus with Modbus RTU protocol.

The cell is amperometric with three electrodes and a constant working voltage, and needs neither a membrane nor reagents. It is meant for circulating-water dosing control, swimming pool chlorination, drinking water treatment and distribution, and hospital effluent.

• •Free chlorine from 0 to 2, 0 to 10 or 0 to 20 mg/L, resolution 0.01 mg/L
• •Three-electrode constant-voltage cell: no membrane and no reagents to replace
• •Integrated design: the RS485 signal leaves the probe itself
• •3/4 in thread at top and bottom, easy to install
• •IP68 protection rating
• •RS485 interface with Modbus RTU protocol
• •Modbus address and baud rate configurable
• •Wide supply range, 7 to 30 V DC

The probe is supplied with a four-core cable with bare ends.

Do not take the colours for granted from memory: not every water probe follows the same convention.

The model code states the range and the electrode. Both are fixed when ordering and cannot be changed afterwards.

• •One integrated residual chlorine transmitter
• •5 m cable (or the length ordered)

• •Submerged installation: run the cable through a rigid waterproof bracket and screw the bracket onto the 3/4 in thread on top of the probe, sealing the thread with PTFE tape.
• •Pipe installation: screw the probe into the pipe through the 3/4 in thread at its lower end.

Two conditions have to be met for the reading to mean anything. The water must be moving past the cell, between 30 and 60 litres an hour in a flow-through fitting: in still water the probe reads its own boundary layer and drifts. And the water must sit between pH 4 and 9, because the share of free chlorine present as hypochlorous acid — the part that disinfects — depends on it. Out of the water the probe reads 0.00 mg/L and stays there; that is normal, not a fault.

• •The equipment needs no routine maintenance. If it fails, do not open it: contact SIGNUX.
• •After use, rinse the head with clean water and fit the protective cover.
• •The platinum wire must stay clean and bright. Dirt or mineral deposits on it lower the sensitivity, and the probe may stop measuring properly.
• •Before measuring, make sure the cell is wet and free of bubbles.
• •The electrode lasts about a year. It is a consumable: replace it when it ages.

If the platinum wire becomes rough or is covered by deposits, clean it according to what has fouled it.

Take care when polishing: the platinum ring is bonded to the glass, and forcing it breaks the cell.

The probe carries two adjustment values: a coefficient A, which multiplies the reading, and a deviation B, which is added to it. From the factory A is 1.0 and B is 0.0.

Both are 32-bit floating-point values, each held in a pair of registers — A in 0x1010 and 0x1011, B in 0x1012 and 0x1013 — and written with function code 16. To move a reading of 7.90 mg/L up to 8.00, the difference of 0.10 is encoded as a float (0x3DCCCCCD) and written to the B pair.

The SIGNUX configuration tool cannot write these two values yet: it does not handle floating-point registers. Until it does, the adjustment has to be made with a Modbus master that can write a float across two registers.

All 16-bit values are sent high byte first. The two floating-point pairs are big-endian: high word in the lower address.

• •UINT16: 16-bit unsigned integer
• •Float: 32-bit IEEE 754, high word first

0x0316 is 790 in decimal, so the concentration is 790 / 100 = 7.90 mg/L.

The probe reads 7.90 mg/L and the reading should be 8.00. The difference is 0.10, which as a 32-bit float is 0x3DCCCCCD. It is written to the B pair, 0x1012 and 0x1013, with function code 16 and two registers in one frame: the high word 0x3DCC first, the low word 0xCCCD second.