Measuring wastewater level and bar screen on/off status in a municipal wastewater treatment plant
In a typical wastewater treatment plant, a mechanical bar screen separates insoluble material like trash and rags from the wastewater stream. Motorized scrapers on each bar screen remove accumulated debris from the screen to maintain a free flow of wastewater into the treatment plant.
An ultrasonic level sensor often controls the scrapers. As the screen clogs, wastewater level rises, and the scrapers are energized to unclog the screen. The scraper motor's on/off status is also usually monitored to ensure that the scraper motor is energized.
I.S. devices for easy installation and maintenance
Municipal wastewater contains methane gas, so the bar screen is potentially located in an I.S. hazardous area. Therefore, the 9106B HART transparent repeater and 9202B Pulse isolator (both I.S. devices) are excellent options.
The PR 9106B safely excites and measures level transmitters located in the hazardous area and provides one or two isolated 4…20 mA outputs.
The PR 9202B can measure contacts or NAMUR sensors located in the hazardous area provides one or two isolated contact or NPN transistor outputs.
Unlike traditional Zener barriers, the PR 9106 and PR 9202 isolated barriers do not require a ground connection in order to make an intrinsically safe measurement of the field device. As our isolated barriers do not require grounding, they are less expensive to install and maintain than Zener barriers. Additionally, the high isolation provided by the PR 9106 and PR 9202 eliminates ground loops and protects downstream devices from high voltage transients and signal noise.
Keep an eye on your devices with the PR 4511
In this application, each module is equipped with a model 4511 Communication enabler. This interface allows easy configuration of the modules and has a backlit LCD screen, making it easy for the plant operator to monitor wastewater level and scraper on/off status from the control panel.
Each PR 4511 also provides Modbus RTU digital communications, which makes it possible for the PR 9106B and PR 9202B isolated barriers to communicate with a Modbus master device.