Chemical Injection / Dosing Using US1000



Chemical addition to a flowing liquid stream is an excellent control application for the US1000-00 Digital Loop Controller. In both water and waste water treatment, chlorine is added as a disinfectant. A residual chlorine analyzer provides the process variable to a closed loop PID controller. A chemical feed pump or gas chlorinator is controlled to maintain the desired chlorine level. The chlorine sensor may be located far downstream of the chemical injector, causing a long lag and deadtime before the desired chlorine level is detected. The inherent delay causes the controller to overshoot and undershoot the set point.

US1000 Control Strategy

The US1000-00 is a cost effective way to control chemical feed systems. To minimize the effects of the time delays, a feed forward flow signal can be applied to sense changes in flow rate and modify the output to the chemical feeder accordingly. This feed forward input can be adjusted for gain and bias. Refer to the block diagram below.

Start up is a snap. The US1000 is pre-configured to accept two 4- 20mADC inputs and transmit a 4- 20mADC control output. Additionally, there is a analog output of the process variable that can be connected to a recorder and three relays for low, high and high-high alarming. A 25.5VDC power supply is available to power the flow meter if desired. A RUN/STOP contact input from a flow switch can turn off the output to the chemical feeder if the flow is interrrupted.

Chemical Dosing Using US1000


Yokogawa's US1000-00 Digital Loop Controller has the versatility to be applied as a chemical feed controller. The feed forward flow input allows open loop (feed forward) control as well as the closed loop PID control action with an analyzer.


Related Products & Solutions


72×144×100 mm sized Digital Indicating Controller has clear bar graph display for PV, SV and MV. It comes with powerful 14 control modes, including optional Custom Computation and dual loop control. The universal input, auto-tuning, "SUPER" functions are standard. Position proportional control and RS485 communication are optionally available.

Single Loop Controllers

Single loop controllers receive temperature, flow rate, pressure, and other types of measurement readings from sensors and send corresponding instructions to control elements such as valves in order to maintain these values within a desired range.


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