Remote Automations Solutions RTU – The Glue Remote Control of Valves

Remote Automations Solutions Remote Control of Valves  SCADA & Communications  Local PID Control Types of Processes Scale Factor Calculation  Valves

Remote Automations Solutions Supervisory Control And Data Acquisition = SCADA Host LocationField Location

Remote Automations Solutions Remote Terminal Units (the glue)  Local Valve Control Custom logic for special cases PID Control

Remote Automations Solutions Commonly Controlled Process  Run Switching Flow Control  Pressure Regulation Pressure Control  Emergency Shutdown Line Break/Leak Detection Leak Detection ON/Off Control

Remote Automations Solutions PID – Type of Process OV Time PV Fast Acting Flow Control Slow Acting Pressure Level Loop OV Time PV

Remote Automations Solutions PID in Simple Terms.  SETPOINT  PROCESS VARIABLE  OUTPUT

Remote Automations Solutions What is the P, I, & D  P is Proportional Gain or Just Gain  I is integral Gain or Reset  D is Derivative Gain or Rate Remote Automation Solutions uses a Scale Factor (SF) that establishes the relationship between the Output and the Process Variable. SF * P represents total Gain Loop Time, the time between start of each PID Calculation

Remote Automations Solutions PID Scale Factor – Why is it so important?  It is the factor in correctly determining the direction of the control action  Major factor in correctly calculating the magnitude of the control action  Reduces the possible range of the proportional gain from -∞ – ∞ to 0.1 – 2.0  If the PID scale factor is not close, tuning a PID control loop becomes a MAJOR trial and error exercise

Remote Automations Solutions PID Scale Factor – How is it Calculated? SF = -1 * ΔOV / ΔPV where: SF = PID Scale factor, in units of OV / units of PV ΔOV = Change in Output Value, in Engineering Units ΔPV = Change in Process Variable, in Engineering Units How are ΔOV and ΔPV determined?

Remote Automations Solutions How are ΔOV and ΔPV determined?? Good – Have the instrument folks tell you the range of the PV that corresponds to the full range of the OV. Be careful about the units and direction. Better – Have operators tell you from their experience what ΔPV is for a given ΔOV. Be careful about the units and direction. Best – With loop in manual mode, adjust the Output Value and observe the value of the Process Variable. ΔOV = OV 2 – OV 1, ΔPV = PV 2 – PV 1

Remote Automations Solutions Scale Factor – Lets Determine It for a Flow Control Loop Best Way – With loop in manual mode, adjust the Output Value and observe the value of the Process Variable. ΔOV = OV 2 – OV 1, ΔPV = PV 2 – PV 1 SF = -1 * ΔOV / ΔPV OV Time PV

Remote Automations Solutions Scale Factor –Level or Pressure Control Best Way – With loop in manual mode, adjust the Output Value and observe the rate of change of the Process Variable. ΔOV = OV 2 – OV 1 ΔPV = (PV 2 – PV 1 ) / (T 2 – T 1 ) * Loop Period where: (T 2 – T 1 ) = Time difference between reading PV 2 and PV 1, in seconds. Loop Period = Time between loop execution, in seconds. SF = -1 * ΔOV / Δ PV OV Time PV

Remote Automations Solutions PID Tuning – Valve Control Enter Calculated Scale Factor Adjust Gain for smooth increase with minimum overshoot Increase Reset for best performance

Remote Automations Solutions Control Valve Selection for Remote Stations

16 Caltrol General Control Valve Selection ANSI Class Pipe Size Material Capacity Rangeability Functionality (control valve vs. regulators)

Remote Automations Solutions Pneumatic or MOV Compressed air or Process Media Communication and Control Fail mode/safety Specifics for Remote Stations

Remote Automations Solutions Pressure reduction to pneumatic actuators Fisher 1301 or 1305  Low Bleed Controllers Fisher FIELDVUE™ DVC When Using Process Media

Remote Automations Solutions  Instrument Air or reduced media Final Assembly Control Signal Feedback/Diagnostics

Remote Automations Solutions Questions