WTW digital IDS pH electrode SenTix 940-3, plastic shaft, 3 m fixed cable, 103741

With a digital IDS electrode, the calibration data is stored in the sensor, not in the measuring instrument. According to the WTW instructions, the electronics in the head store the sensor type, serial number and the last 10 calibrations. As a result, the correct slope and asymmetry automatically apply on the connected measuring instrument, and several calibrated sensors can be swapped on one instrument without recalibration. The WTW SenTix 940-3 has a gel electrolyte and a plastic shaft.

Gel without refilling

The shaft is made of PPE/PS, is 120 mm long and has a diameter of 12 mm. The gel electrolyte is not refilled, and the electrode is low-maintenance. According to WTW, the fibre junction prevents blockages. The membrane is cylindrical, and according to the product page its resistance is below 1 GΩ. It measures from 0 to 14 pH at sample temperatures of 0 to 80 °C.

Temperature recorded at the same time

An NTC temperature sensor (30 kΩ) is built in, so a second sensor in the sample vessel is not needed. According to WTW, the IDS measuring electronics work with an accuracy of pH ±0.004, ±0.2 mV, ±0.1 °C (±1 digit in each case).

Typical applications according to WTW

• Swimming pool water
• Wastewater in general, industrial wastewater and electroplating wastewater
• Groundwater
• Lake water, surface water and seawater

Connection to the measuring instrument

The SenTix 940-3 has a permanently attached cable of 3 m. The IDS plug is a 4-pin, waterproof plug connection with locking. The versions 940, 940-3 and 940-P have the same electrode and differ only in the connection. Which one is suitable depends on the distance between the sample and the measuring instrument.

Storage

Before the first measurement, the wetting cap is removed, and gas bubbles behind the membrane are removed by shaking. During short breaks, the electrode is immersed in reference electrolyte (KCl 3 mol/l, Ag+-free); overnight and for longer, it stays in the wetting cap filled with it. If stored dry or in deionised water, it can be permanently damaged according to WTW. If the liquid in the cap has dried out, the electrode needs at least 24 hours in reference electrolyte. Strong acids and alkalis, hydrofluoric acid, organic solvents, oils, fats and proteins shorten the service life, as with any pH electrode.

Technical details

Scope of delivery

• 1 WTW SenTix 940-3 pH electrode with wetting cap
• Operating instructions
• Fixed cable 3 m with IDS plug, permanently attached to the electrode

Regulatory information

As an electrical device, the digital IDS electrode falls under the ElektroG. The manufacturer Xylem Analytics Germany GmbH (WTW brand) is registered under the WEEE registration number DE 29884659. How to return old appliances is described on the page Environment and disposal.

Accessories and procurement service

Also available are reference electrolyte KCl 3 mol/l for the wetting cap and buffer solutions for calibration. For other IDS electrodes or larger quantities, there is the procurement service.