MechChem Africa September-October 2023

⎪ Automation, hydraulics and pneumatic systems ⎪

The trend in filter monitoring From preventive maintenance to Industry 4.0 and IIoT cloud solutions, there is a demand for data everywhere. This can be seen clearly in the change from traditional measuring instru ments with optical displays to electrical sensors with analogue or digital output signals. When monitoring pressure filters, we see a trend to replace differential pressure sensors with gauge pressure sensors before and after the filter. This gives both the system pressure and the pressure at the outlet of the filter, which a differential pressure sensor does not offer. The pressure drop, the difference between the two signals, is then cal culated by the electronic controller, by the edge computer or in the cloud. In addition to pressure sensors for filter monitoring, the WIKA portfolio covers all relevant measurement pa rameters that are necessary for con trolling and regulating the operating states of a machine or system. Further application examples can be found on our website in the ‘Industries’ pages. www.wika.com/en-en/industries.

flows back into the tank. There is ambient pressure (atmospheric pressure) in the tank. This means that ambient pressure is also present at the filter outlet. This simplifies monitoring since a differential pressure sensor can now take over the measuring task. This has a favourable effect on the costs of filter monitoring. First, differential pressure sensors are less expensive than ΔP sensor. Also, there is a saving on the need for a pressure line from the filter outlet to the low-pressure connection of the ΔP sensor. In addition, temperature measurement of the oil is essential in hydraulic circuits. This enables the high viscosity of the hy draulic oil, which is still cold when starting, to be considered, thus avoiding false alerts. The hydraulic oil temperature is also required to control the oil cooler. It has a significant influence on the time over which the oil is used.

out the filters only happens when the filter is close to reaching its accepted level of contamination. A further advantage is that through continuous monitoring and track ing, the filter replacement can be scheduled for the convenient and cost-effective shut down time of the operational process. In either case, the pressure drop across the filter is measured, that is, the change in pressure (ΔP) between the filter inlet and outlet. However, the pressure loss across the filter also increases with the volume flow. The ΔP as an indicator of the contami nation of the filter may therefore only be assessed in the defined operating state (average flow and temperature). Filters for liquids can exceed the ΔP limit because of brief pressure peaks, for example. Due to inertia, however, these are not problematic issues for mechanical switches. For sensors, however, it is advisable to provide for a short ‘dead time’ in the elec tronic control system to smooth out any transient measurements. Filter monitoring in hydraulic circuits The return filters in a hydraulic circuit are a special case. As the name suggests, these are in the return line, just before the oil

The formula for calculating excessive differential pressure due to the high viscosity of cold oil.

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