Multimedia filter
Isolation / conversion
The multimedia filter is used to reduce the level of suspended solids (turbidity) in incoming feed water.
Unlike traditional sand filters, multi-media water filters are composed of three filtration media, ordered in decreasing porosity. Because of their multi-layer design, multi-media water filters are able to trap and retain a far larger number of particles than traditional sand filters before backwashing becomes necessary. The process of multimedia filtration produces high quality, filtered water at much faster flow rates than traditional sand filtration. Pressure measurements in the multimedia filtration system are very important because of head loss.
As the water flows through the media, solids are trapped, increasing head pressure and decreasing flow. Eventually, the flow drops to a point where the filter must be cleaned.
A differential pressure transmitter is used to measure when the backwash should be initiated.
The DP transmitter is powered, measured, and isolated by the 9116A universal converter. The 9116A can detect any error on the 4...20 mA input signal and set a relay contact output. The 9116A can convert an active DP transmitter to a passive 4...20 mA output signal.
Application:
> Need more information? Please contact us.
What is a multimedia filter and how does differential pressure monitoring work with PR Electronics?
A multimedia filter uses layered beds of sand, gravel, and anthracite to remove suspended solids from water. Differential pressure across the filter bed increases as particles accumulate — when DP reaches a threshold, backwash is initiated to clean the media. The PR 9116A Universal Converter receives the DP transmitter signal, provides galvanic isolation, and includes a programmable relay output that can trigger the backwash sequence automatically when the DP setpoint is reached. This ensures timely backwashing to maintain filter performance without operator intervention.
How does the PR 9116A Universal Converter support multimedia filtration monitoring?
The PR 9116A accepts the 4-20 mA signal from the DP transmitter monitoring filter bed pressure drop and converts it to an isolated output for the PLC/SCADA system. Its programmable relay output can be configured to activate when the DP exceeds the backwash initiation setpoint — typically around 10-15 psi depending on filter design. The device also monitors the signal for transmitter failure (line break or out-of-range), providing a separate alarm for instrumentation faults. SIL 2 certification ensures it meets the safety requirements for automated filtration control.
What are the benefits of automated backwash initiation based on differential pressure measurement?
Automated backwash based on actual filter DP — rather than fixed time intervals — optimizes water production by only backwashing when needed. This saves backwash water (typically 2-5% of production), reduces energy costs for backwash pumps, and extends filter media life. The PR 9116A provides the reliable signal conditioning and relay alarm function needed to implement DP-based backwash automation, converting the DP transmitter signal to both an analog output for trending and a discrete relay output for backwash valve control.
