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Sep 21, 2007

Coolant monitor protects refrigeration circuits

© Reuse this Cooling manufacturer Jumo Aquis has developed the new Jumo Aquis 500 series with an electrode as an economical system to detect ammonia. Owing to its good thermodynamic properties, ammonia is often used as a coolant, not only in small refrigeration systems, but also in large industrial plants. However, ammonia is a corrosive and poisonous chemical and, as it can be a potential hazard, requires continuous monitor- ing. This is even more important if the plant concerned is being supplied with water from rivers or open waters.

Most refrigeration systems consist of a primary circuit, with ammonia, and a secondary circuit. The secondary circuit usually contains a mix of water and glycol or some other mixture. There can be a potential risk of leakage at the interface between the primary and secondary circuits, for instance the refrigeration piping can corrode. If this piping is made from copper, the wall thickness of the pipe may become so thinned by the chemical reaction of the copper with the ammonia that a hole occurs.

The ion-sensitive sensor of the Jumo Aquis 500 operates over a range of 0,01 mg/8467 to 20g/8467 and consists of a pH glass electrode and a reference electrode. Both electrodes are immersed in a special electrolyte. A membrane that is permeable to ammonia separates the pH and reference electrodes from the medium being measured.

The presence of ammonia in the sample medium is strongly dependent on the pH value. In the acidic range, there will be a predominance of ammonium ions (NH4+), which are not detected by the sensor. In order to achieve optimum detection of the ammonia, the Jumo has a special flow-through fitting for the ammonia sensor. This facilitates quick and easy connection of the sensor according to the process setup.

The corresponding transmitter/controller is easy to use through the simple menu-led opera-tion. In the normal display setting, the Jumo Aquis 500 shows the principal measurement and the temperature, either as a numerical display or as a bar graph. A trend indicator can also be activated.

The high level of enclosure protection allows the instrument to be used either as a panel- mounted instrument or as an on-site measuring device. Condensation in the electronics is prevented by a diffusion-open membrane. All versions can be fitted with up to two electrically isolated analog outputs, for 4 mV to 20 mV or 0 V to 10 V, as process value or control outputs. The type of output and the scaling are freely programmable.

Two additional outputs can be fitted with changeover relays. These relays enable simple limit monitoring as well as a more demanding PID control loop function. Three power supply versions permit operation with typical supply voltages of 12 V dc, 20 V to 53 V ac/dc and 110 V to 240 V ac.
Edited by: Laura Tyrer
© Reuse this Comment Guidelines (150 word limit)
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