Monitoring chemical flow and tank level in a wastewater treatment process
One of the first steps in treating municipal wastewater is separating sludge from the wastewater liquid. To speed up this separation process, a chemical flocculant like Aluminum Sulfate is added to the wastewater. A flocculant helps particles of sludge clump together and fall to the bottom of the settling basin, while the wastewater liquid remains on top.
The chemical flocculant is stored in a tank, and the level of the chemical is measured. The flowrate of flocculant into the wastewater stream is also measured to ensure correct dosing. If too little flocculant is added to the wastewater, the sludge will not completely separate from the liquid. Adding too much flocculant wastes money, and can also reduce the effectiveness of the flocculant.
Flexibility and isolation with the PR 9000 series
The model 9106 HART transparent repeater can be used to excite and measure the flocculant dosing flowmeter. The PR 9106 can output two isolated 4…20 mA signals. In this application, one signal goes to a local HMI, and the other signal goes to a chart recorder.
A 9202 Pulse isolator can be used to measure the flocculant storage tank float switches, providing isolation and protecting the controller digital inputs from voltage transients and ground loops.
The PR 9106 is very flexible – capable of measuring active or passive current inputs and delivering active or passive current outputs. The PR 9202 measures contact or NAMUR sensor signals, and is available in versions with normally open or normally closed contact outputs, or NPN transistor outputs. I.S. versions of the PR 9106 and PR 9202 are available for measuring sensors located in Division 1/zone 0 locations.
In this application, the PR 9106 and PR 9202 modules can be equipped with the 4511 Communication enabler. This detachable interface communicates via Modbus RTU, allowing a Modbus Master to monitor easily each module's I/O and status. The PR 4511 display shows a unique 5-digit tag number, and provides easy-to-understand error messages in case of a module or sensor failure.