Pumps and Systems, June 2009
Editor's Note: Click here to read an article from the June 2009 issue about digital dosing pumps and maintaining metering pump accuracy. |
Digital dosing pumps can receive an analog signal from an analyzer, PLC or similar instrument, and in the event of a significant change in the total system requirements for the chemical being dosed, reprogramming the internal software can change the maximum volume the pump can deliver. In addition to the 800:1 turn down ratio, the electronic controls on board will allow the operator to scale on both ends (4 and 20mA), to enable a proportional injection in a specific range. For example, in the case where 5mA= 2 gallons per hour and 15mA = 6 gallons per hour, the digital electronics of the pump will adjust the scale and speed within the capacity range to deliver what the operator inputs on the control pad. While other metering pumps can take the analog signal, only digital dosing pumps offer the electronics to auto-compensate and self correct. A digital dosing pump has the flexibility to re-scale on both ends of the signal, so it can be easily integrated to the PLC or SCADA system without the need for external devices.
Digital pumps can also provide the necessary feedback signals such as analog 4-20 mA, alarm contact and pulse signal to close the control loop or implement master/slave configurations. This important feature, normally available only on process controllers, is part of the brain of this type of these instruments.