Methods and apparatus for operating and performing diagnostics in a control loop of a control valve

A method of selectively operating a control loop for a control valve in either a travel control mode or a pressure control mode, wherein the control valve has a throttling element coupled to a pneumatically operated actuator defining at least a first control chamber, and in which the control loop includes a pneumatic amplifier having an inlet port in fluid communication with a supply of control fluid, a first outlet port in fluid communication with the actuator first control chamber, and a control fluid valve assembly responsive to a control pressure signal for controlling flow of control fluid between the inlet port and the first outlet port;

• and an I/P converter adapted to receive an I/P drive signal and generate the control pressure signal;
• the method comprising:
• operating the control loop in travel control mode by:
• storing a reference travel signal;
• generating the I/P drive signal based on the reference travel signal;
• receiving a measurement of a throttling element travel value corresponding to a position of the throttling element;
• comparing the measured throttling element travel value to the reference travel signal to generate a travel error signal;
• and
• modifying the I/P drive signal based on the travel error signal;
• and
• operating the control loop in pressure control mode by:
• storing a reference outlet pressure signal;
• generating the I/P drive signal based on the reference outlet pressure signal;
• receiving a measurement of a first outlet port pressure level of control fluid at the pneumatic amplifier first outlet port;
• comparing the measured first outlet port pressure level to the reference outlet pressure signal to generate a outlet pressure error signal;
• and
• modifying the I/P drive signal based on the outlet pressure error signal.

A positioner system adapted to control a pneumatic actuator coupled to a throttling element, the actuator having at least a first control chamber, the positioner system comprising:

• a processor and a memory, the processor adapted to receive an outlet pressure set point and generate an I/P drive signal;
• an I/P converter operatively coupled to the processor and adapted to generate a pneumatic control signal in response to the I/P drive signal;
• a pneumatic amplifier operatively coupled to the I/P converter, the pneumatic amplifier having an inlet port in fluid communication with a supply of control fluid, a first outlet port in fluid communication with the actuator first control chamber, and a control fluid valve assembly adapted to control flow of control fluid from the inlet port to the first outlet port in response to the pneumatic control signal;
• and
• a first outlet port pressure sensor adapted to detect a pressure level at the first outlet port and generate a first outlet port pressure signal, wherein the first outlet port pressure sensor is communicatively coupled to the processor;
• wherein the processor is adapted to compare the first outlet port pressure signal to the outlet pressure set point and generate an outlet pressure error signal, and wherein the processor is adapted to modify the I/P drive signal based on the outlet pressure error signal.

A positioner system adapted to control a pneumatic actuator coupled to a throttling element, the actuator having at least a first control chamber, the positioner system comprising:

• a processor and a memory, the processor adapted to receive a travel set point and an outlet pressure set point and generate an I/P drive signal based on at least one of the travel and outlet pressure set points;
• an I/P converter operatively coupled to the processor and responsive to the I/P drive signal to generate a pneumatic control signal;
• a pneumatic amplifier operatively coupled to the I/P converter, the pneumatic amplifier having an inlet port in fluid communication with a supply of control fluid, a first outlet port in fluid communication with the actuator first control chamber, and a control fluid valve assembly responsive to the pneumatic control signal to control flow of control fluid from the inlet port to the first outlet port;
• a first outlet port pressure sensor adapted to detect a pressure level at the first outlet port and generate a first outlet port pressure signal, wherein the first outlet port pressure sensor is communicatively coupled to the processor;
• and
• a throttling element travel sensor adapted to detect a position of the throttling element and generate a throttling element position signal, wherein the throttling element travel sensor is communicatively coupled to the processor;
• wherein the processor is adapted to operate in a travel control mode in which, the throttling element position signal is compared to the travel set point to generate a travel error signal, wherein the I/P drive signal is modified by the travel error signal, and in a pressure control mode in which the first outlet port pressure signal is compared to the outlet pressure set point to generate an outlet pressure error signal, wherein the I/P drive signal is modified by the outlet pressure error signal.

A method of detecting faults in a control loop for a control valve having a throttling element coupled to a pneumatically operated actuator, the control loop including a pneumatic amplifier operatively coupled to the actuator and having a control fluid valve assembly responsive to a control pressure signal for controlling flow of control fluid to the actuator, and an I/P converter operatively coupled to the pneumatic amplifier for generating the control pressure signal in response to an I/P drive signal, wherein the I/P drive signal is based on a reference outlet pressure signal, the method comprising:

• storing a normal range for a control parameter of the control loop;
• triggering a fault signal for operation of the control parameter outside the normal range;
• characterizing operating parameters of the control loop during the fault signal to derive a fault template;
• comparing the fault template to sets of stored operating parameters associated with specific component failures;
• and
• identifying at least one specific component failure having a set of stored operating parameters that matches the fault template.

A positioner system adapted to control a pneumatic actuator coupled to a throttling element, the actuator having at least a first control chamber, the positioner system comprising:

• a processor and a memory, the processor receiving an outlet pressure set point and generating an I/P drive signal;
• an I/P converter operatively coupled to the processor and responsive to the I/P drive signal to generate a pneumatic control signal;
• a pneumatic amplifier operatively coupled to the I/P converter, the pneumatic amplifier having an inlet port in fluid communication with a supply of control fluid, a first outlet port in fluid communication with the actuator first control chamber, and a control fluid valve assembly adapted to control flow of control fluid from the inlet port to the first outlet port in response to the pneumatic control signal;
• a first outlet port pressure sensor adapted to detect a pressure level at the first outlet port and generate a first outlet port pressure signal, wherein the first outlet port pressure sensor is communicatively coupled to the processor, wherein the processor is adapted to compare the first outlet port pressure signal to the outlet pressure set point and generate an outlet pressure error signal, and wherein the processor is adapted to modify the I/P drive signal based on the outlet pressure error signal;
• a second sensor communicatively coupled to the processor and adapted to detect a control parameter of the positioner system;
• and
• a diagnostics routine stored in the memory and adapted to be executed on diagnostics information based on at least one diagnostics parameter selected from the group of parameters including the first outlet port pressure level and the control parameter
• wherein the processor is further adapted to compare the first outlet port pressure signal and the outlet pressure set point to generate an outlet pressure error signal, and wherein the processor is adapted to modify the I/P drive signal based on the outlet pressure error signal.