PROCESS CONTROL SYSTEMS LAP 4 Loop Controllers. Notes

Transcription

1 PROCESS CONTROL SYSTEMS LAP 4 Loop Controllers Notes 1) Loop Controllers a) Two categories of loop controllers (1) Pneumatic controllers (a) Use air inputs/outputs to sense the process variable and send error signals to correct for process disturbances (b) Used when the use of electricity could pose a safety concern (i) Explosive environments (c) Also used in remote locations where electrical access may be a problem (2) Electronic controllers (a) Use electrical inputs/outputs to sense the process variable and send error signals to correct for process disturbances (b) The most widely used and diverse type of controllers in use today (i) Very accurate (ii) Fast processing time (iii)reliable and easy to maintain (iv) Flexible configuration (c) Includes PLCs and computers b) Four basic control functions of an electronic loop controller i) Manual control (1) Operator is responsible for adjusting the output signal to meet process demand ii) On/Off (1) The most basic control mode

2 (2) Used when precise control is not required, only that the process variable is maintained within a range of values iii) Automatic control (1) The most commonly used function of a controller (2) The controller automatically adjusts the output to maintain the process variable at the setpoint based on sensor input iv) Alarms (1) Alert the operator of abnormal conditions in the process c) Major components of an electronic loop controller i) Display panel (1) Mode Auto/Manual (2) Function- displays current status of alarms, inputs, outputs (3) Units (a) F/C ii) Control panel (1) Typical buttons include: (a) Setup key (i) Allows access to programming functions an menu navigation (b) Func Loop 1/2 key (i) Allows navigation through the different parameters of within a selected programming group (c) Lower display key (i) Toggles between Normal and Setup display modes (ii) In Normal mode toggles the displayed value in the lower part of the display (d) Manual/Auto key

3 (i) Selects mode of operation (e) SP Select key (i) Chooses the desired setpoint (f) Run/Hold key (i) Allows the operator to start or hold a setpoint program (g) Up/Down key (i) Change parameter values and scroll through menus (h) Communication port (i) Infrared, Ethernet, serial, USB, etc. iii) Body (1) Physical housing iv) Connection terminals (1) The interface to the process components d) Introduction to the Honeywell UDC 3500 controller i) Power up and determine operating status (1) No on/off switch hardwired to power source (2) Diagnostic routines end with a Test Done message on the display (3) Failure of any diagnostic test results in going to FAILSAFE manual mode (a) Diagnostic messages may be displayed ii) Two display modes of the UDC 3500 controller (1) Control display mode (a) Normal operation (b) Displays the PV, SP, Output, and deviation (2) Setup display mode (a) Accessed during configuration (b) Allows the operator to view and change the controller setup parameters (i) Controller continues to operate under previously stored settings

4 (ii) If the controller has never been programmed, the controller operates according to the factory default settings iii) Navigating the UDC 3500 controller menu system (1) Enter the setup menu (2) Use the Func Loop 1/2 key to scroll through all of the parameters in the group (3) Use the Up/Down arrows to change a parameter (4) Return to the Control display mode by pushing the Lower Display key 2) Loop Controller Parameters a) Parameter groups (see page 38) i) Tuning group (1) Proportional, Integral, Derivative and assosciated ii) Input group (1) Information about the input devices and signals to the controller (a) 4-20 ma, 0-20 ma, 0-5 V, etc (b) Transmitter type iii) Control group (1) Setpoint limits (2) Deadband iv) Alarm group (1) Type of alarm and its associated process variable v) Options group (1) Additional I/O (2) Added functionality b) Viewing and interpreting controller process variables i) Control display mode (1) View status of PV and SP ii) Manual mode

5 (1) PV and output value (in percent) (a) 0% = 4 ma 100% = 20 ma c) Enter a loop controller parameter using the control panel keys i) Enter the Setup menu ii) Scroll to the desired parameter group iii) Use the Func 1/2 key to scroll through parameters in the selected parameter group iv) Use the Up/Down arrow keys to adjust the parameter value v) Return to the control display mode d) Restoring factory default settings on the Honeywell UDC 3500 controller i) Power up the controller ii) Press the Func Loop 1/2 and the Up arrow keys simultaneously while TEST DONE is displayed to enter restoration mode iii) Press the Func Loop 1/2 to enter the RESTORE menu and use the Up arrow key to select CFG RESTORE iv) Press the Func Loop 1/2 key to initiate the restoration (1) DOING RESTORE will be displayed v) Controller will automatically return to the control display mode when done 3) Manual Operation a) Generally behaves as an open loop system b) Operator intervention is required to make adjustments to the process c) Connecting a loop controller to a final control element i) Connect the controller analog (4-20 ma) output to the final control element analog (4-20 ma) input

6 ii) To change a 4-20 ma current signal to a 1-5 volt signal connect a resistor across the input terminals of the final control device (1) Ohm s Law can be used to determine the resistor value (a).004 ma X 250 ohms = 1V (b).020 ma X 250 ohms = 5V d) Honeywell UDC 3500 Manual mode i) Place the controller in Manual mode ii) Press the Lower Display key to view the controller output iii) Use the Up/Down arrow keys to adjust the output as necessary iv) Press the Lower Display key to toggle between the setpoint, deviation value, and output