What typically happens after a control motor receives a small increase of the input signal from the temperature controller? Nothing.

Further increases of the 4-20 mA signal also produce no control motor movement. An additional input signal increase and the motor drives by 4 or 5 degrees. This modulates the burner from a 40:1 turndown to approximately a 6:1 turndown. The result may be poor product quality through a lack of precise temperature control.

Many companies have modernized their combustion control panels to the latest technology, including PLCs, touchscreens and linkage-less burner controls. For all these advancements, the most economical way to gain control of your temperature is to improve the precision of the device that modulates the gas flow to the burner -- the control motor.

The most modern control motor technology offers significantly increased modulating accuracy and resolution. Utilizing the entire input signal by adjusting the zero and span allows full use of the entire 4-20 mA range across the selected range of movement. Control motors with internal double offset gearing in both the actuator and the potentiometer ensure minimal shaft play.

Improved modulating resolution and accuracy is found in control motors utilizing precise resistive plastic potentiometers instead of wire-wound versions that limit the number of control steps. Industrial motors with fully encapsulated potentiometers are not as susceptible to the dust and corrosives typically found in manufacturing environments. Control motors with internal resistive plastic potentiometers offer significantly increased accuracy and resolution.

The latest in control motor technology offers an internal linearization function to enhance modulating accuracy. PID control parameters can be adjusted for tighter control. The linearization feature compensates the movement of the actuator in response to a modulating input signal step change. The result is a step change in burner capacity, not a step change in actuator position. For example, at 80 degrees open, an actuator with a linearization function enabled might move 4/10 of a degree in response to a step change. The same step change may result in only a 1/10 of a degree movement if the actuator was at low fire. A control motor with an internal linearization function provides equal flow changes for similar input signal changes. The result is greater modulating control where it is needed the most -- at lower burner capacities.

Many of today's advanced controllers utilize feedback signals such as 1,000 Ohm, 4-20 mA, or 0-10 VDC. The latest control motors allow various possible feedback signals including representing the actual shaft position for slaving. The feedback feature may be used to control other actuators either in parallel or slave mode.

Accurate and precise motors allow temperature control to be achieved in industrial ovens and furnaces applications for reduced energy consumption and better production results.

Sidebar
Motor Control At a Glance

The most economical way to gain control of your temperature is to improve the precision of the device that modulates the gas flow to the burner -- the control motor.

  • Get significantly increased modulating accuracy and resolution with the most modern control motor technology.

  • Utilize the entire input signal of modern control motors by adjusting the zero and span for full use of the entire 4-20 mA range across the selected range of movement.

  • Ensure minimal shaft play by using control motors with internal double offset gearing in both the actuator and the potentiometer.

  • Look at the latest in control motor technology for an internal linearization function that enhances modulating accuracy.

  • Benefit from how a linearization feature compensates the movement of the actuator in response to a modulating input signal step change.

  • Learn how the latest control motors allow various possible feedback signals including representing the actual shaft.


For more information

Contact Siemens Combustion Controls (formerly Siemens Building Technologies, Combustion Products). Call (877) 891-1605, or visit www.scccombustion.com.

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