If the careful usage of ?energy? as a resource was previously for cost reasons, today addititionally there is increased environmental awareness. All this also becomes mandatory thanks to legal requirements and the state of the technology. In the following paragraphs you can read about how continuous filter monitoring crucially influences the power efficiency of a system and supports you in complying with legal requirements.
Comparison: New filter ? used filter
Whether with air filters in ventilation and air-conditioning systems or oil filters in hydraulic circuits, in both cases, increasing contamination of the filter element causes an increasing pressure drop. In order to keep the flow of the medium (air or oil) constant, the fan or the pump (respectively) must apply more power. The power consumption increases. Filter monitoring signals the increasing pressure drop across a contaminated filter element. Replacing a fouled filter ensures the flow of the medium and thus prevents the energy consumption of the fan or the pump from increasing.
Legal bases
With the adoption of the Kyoto Protocol in 1997, the European Union committed itself to reducing CO2 emissions. So as to reach this climate goal, in 2005 it adopted the EuP (Energy using Products) directive. In 2009 2009, this was renamed the ErP directive (Energy-related Products directive) ? also known as the Ecodesign directive.
Pressure gauge with switch contact, model PGS21
High resistance ? high energy consumption
It is easy to recognize that a contaminated filter element is more resistant to the flow of a medium when compared to a new, clean element. Physically, the pressure in the inlet (filter inlet) increases ? which is often monitored very well utilizing a pressure measuring instrument ? and the flow rate is reduced. Since the required flow is specified, more energy must be introduced to compensate for the restriction in the filter.
Costs of filter change
Energy-related vs. cost-based considerations
From an energetic viewpoint, a lightly soiled filter should be replaced straight away. This conflicts with the fact that the exchange itself generates material and labour costs. In addition, the exchange can only take place in the absence of both pressure and flow, and therefore the machine or the procedure must be stopped. Based on these considerations, it is also clear an exchange following a fixed amount of use, as we are familiar with annual services on cars, for instance, isn’t an optimal solution.
Compromise: Filter monitoring
The compromise is an acceptable degree of contamination ? meaning a specified maximum differential pressure across the filter. Normal limit values for the differential pressure (?P) of a hydraulic filter are between 1 and 5 bar. In ventilation systems, the limit values are between 50 to 5,000 Pa (0.5 to 50 mbar). Monitoring the pressure drop saves on operating costs, since changing out the filters only happens when near reaching the accepted level of contamination of the filter. A further advantage is that, through continuous monitoring, the filter replacement can be scheduled in to the operational process.
Filter monitoring through measuring the pressure drop
In each case, the pressure drop over the filter is measured ? so ?P between the filter inlet and outlet. However, the pressure loss over the filter also increases with the volume flow. The ?P as a indicator of the contamination of the filter may therefore only be assessed in the defined operating state (flow and medium temperature). Filters for liquids can exceed the ?P limit because of brief pressure peaks. Because of inertia, these are no problem for mechanical switches. For sensors, it is advisable to give a short dead time in the electronic evaluation (control).
Special case: Filter monitoring in hydraulic circuits
The return filters in a hydraulic circuit are a special case. Because the name suggests, these are in the return line, right before the oil flows back into the tank. There’s ambient pressure (atmospheric pressure) in the tank. This means that ambient pressure can be present at the filter outlet. This simplifies monitoring, since a differential pressure sensor is now able to take over the measuring task. It has a favourable effect on the costs of filter monitoring. On the one hand, these pressure sensors are less expensive than differential pressure sensors. Alternatively, you save on needing a pressure line from the filter outlet to the low-pressure connection of the ?P sensor. Temperature measurement of the oil is essential in hydraulic circuits. This enables the high viscosity of the hydraulic oil, that is still cold when starting, to be taken into consideration, thus avoiding false alerts. The hydraulic oil temperature must control the oil cooler. It includes a significant influence on the time over that your oil is used.
Calculation of the excessive differential pressure as a result of high viscosity of cold oil
The trend in filter monitoring
Pressure sensor A-1200 with IO-Link
From ?preventive maintenance? to ?Industry 4.0? to IIoT cloud solutions ? you will find a demand for data everywhere. This is often seen clearly in the change from traditional measuring instruments with optical displays to electrical sensors with analogue or digital output signals. When monitoring pressure filters, we are able to see the trend to replace the differential pressure sensor with gauge pressure sensors before and after the filter. Thus giving one 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 calculated in the electronic control, in the edge computer or in the cloud.
Note
As well as pressure sensors for filter monitoring, the WIKA portfolio covers all relevant measurement parameters that are necessary for controlling and regulating the operating states of a machine or system. Further application examples can be found on our website in the ?Industries? section.
Also read our article
Safe filter monitoring with differential pressure gauge s