INSTRUMENTATION • ELECTRONICS
Advanced actuators Katie Wilson outlines a compact actuation solution for chemical dosing D
esigned for quarter-turn, rotary or linear operation, Rotork CMA actuators perform numerous process control valve, metering pump and damper applications demanding precise position control and continuous
modulation. Single-phase or DC electrical power is all that is required for simplifi ed installation and control valve actuation. Explosion-proof certifi cation to international standards is available for hazardous area applications. In a recent application CMA actuators have delivered
a reliable, compact solution for a new chemical dosing application at a water treatment plant expansion at the City of Loveland, Colorado USA. T e chemical dosing skids are part of a new chemical storage building, housing two giant tanks with a capacity of 46 million gallons per day (MGD). Operating mostly CPVC ball valves and some 4in
butterfl y valves on the chemical feed pump main and bypass lines, 21 CMQ 500 actuators control the delivery of chemicals to the various processes. T e skid-mounted valves and pumps control the dosing of alum, polymer, sodium hypochlorite, fl uoride, chlorine dioxide and sodium bisulphite.
LOCAL CONTROLS Local controls on the actuators contributed to their selection, being a possibly unique feature of the compact CMA design. T ey provide manual operation at the valve, combined with an LCD display of valve position that also incorporates critical and non-critical fault symbols. Control knobs enable selection of Local, Stop or Remote
operation and Open or Close input commands in the Local control mode. Each mode can be locked in place to prevent unauthorised operation. T e LCD display shows the valve position as a precise percentage of total valve travel.
MAINTENANCE-FREE T e maintenance-free CMA drivetrain, environmentally
protected to IP67 and permanently lubricated for operation in sub-zero temperatures as
standard, can be mounted in any orientation. Accepting an industry-standard 4-20mA control signal, the CMA provides accurate, repeatable and backlash- free positional control. Resolution is 0.2% on linear and quarter- turn applications and 2 degrees on the multi-turn models. All CMA actuators have output speeds that are adjustable down to 50% of full speed in 10% increments and
manual operation is provided as standard. Network compatibility encompasses Rotork Pakscan, HART, Profi bus, Modbus, DeviceNet and Foundation Fieldbus.
FAILSAFE
When fail-to-position performance is required, a reserve power pack provides the actuator with the ability to perform a predetermined action on power failure. T e power pack also preserves position indication on the LCD display during power failure. When mains power is restored, the power pack is quickly recharged to ensure continued fail-to-position functionality. Action on power loss is easily confi gured with the standard CMA HMI interface as part of the user-friendly actuator set-up menu, utilising a 6-segment LCD display and push button confi guration. ■
Katie Wilson is with Rotork.
www.rotork.com
48
www.engineerlive.com
Above: The actuators are designed for process control valve, metering pump and damper applications
Left: Rotork CMA process control actuators deliver a reliable, compact solution for chemical dosing applications at a water treatment plant in Colorado
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52