Extech Instruments 48VFL User Manual

16 VFL Series User Manual v2.3 12/20
PID control minimizes setpoint overshoot, oscillations, and disturbances in a process by
throttling the controller output automatically. The controller must first be tuned so that it
understands the speed and dynamics of the process. See the Auto Tune section.
Proportional-only control adjusts the controller output, proportional to the proximity of PV to
SV. The closer to setpoint, the lower the output %. The further from setpoint, the higher the
output %.
Proportional-only control, however, has a side effect (known as droop or offset) where the
process is brought to equilibrium, but not exactly at setpoint. This is where Integral control is
useful, as it checks for droop as often as you specify in the ‘ti’ parameter (Menu 3, PID).
Proportional-Integral (PI) control is fine for systems where there are no sudden process
changes expected. In cases where sudden changes to process are possible (or even frequent),
then Derivative control can be used.
Derivative control (‘td’ in Menu 3, PID) is known as anticipatory control, as it looks at the rate
of change in a process and makes output adjustments to prevent process disturbances.
It calculates where the process will be at some point in the future, given the present rate of
change, and uses that information to determine the output adjustment needed.
6.10 PID ‘Time Proportioning’ Control
PID control is easy to picture with a linear analog output, where a 4 to 20mA output, for
example, responds linearly to the 0 to 100% control output variations. 0% power = 4ma, 50%
power = 12ma, 100% = 20mA, and so on.
A relay, however, is very different from a linear analog output in that it has only two states, ON
and OFF, where the 4 to 20 signal is continuous throughout its range. So, to apply PID control
to a relay, Time Proportioning PID control is used.
Time Proportioning adjusts the ratio of relay ON-time to relay OFF-time, over an adjustable
time duration, known as the Cycle Time (‘ct’ parameter in Menu 3, PID).
The controller ‘throttles’ the output relay, keeping the relay ON longer, when the PV is further
from SV, and OFF longer, when the PV is close to the SV.
The ratio of relay ON-time to relay OFF-time is automatically adjusted at the start of each Cycle
Time window, based on PV/SV proximity.
Time Proportioning control is active when the Proportional Band ‘Pb’ (or Cooling Proportional
Band ‘CPb’) parameter is set to some value other than ‘0’ in Menu 3, PID.
The examples below illustrate three stages in a process where the output % is changed, based
on process conditions.

Extech Instruments 48VFL Specifications

General

Brand	Extech Instruments
Model	48VFL
Category	Controller
Language	English

Summary

Introduction to Extech VFL Process Controllers

Safety Precautions for Extech Process Controllers

Panel Mounting and Dimensions

48VFL Controller Mounting

Instructions for mounting the 48VFL controller into a panel.

96VFL Controller Mounting

Instructions for mounting the 96VFL controller into a panel.

Wiring Guide for Extech VFL Controllers

Important Safety Wiring Considerations

Crucial safety guidelines for wiring the controller and associated equipment.

AC Power Wiring

Details on connecting AC power to the 96VFL and 48VFL controllers.

Thermocouple Input Wiring

Wiring instructions for thermocouple inputs on the 96VFL and 48VFL.

Analog Input (4-20mA) Wiring

Wiring details for optional 4-20mA analog inputs.

RTD Input Wiring

Wiring guide for RTD inputs, covering 2, 3, and 4-wire configurations.

Control Relay Wiring

Explanation of how to wire control relay outputs (OUT 1 and optional OUT 2).

Pulsed DC Trigger Output Wiring

Instructions for wiring the pulsed DC trigger output option.

Analog Output Wiring

Details on wiring the optional analog output (4-20mA).

Alarm Relay Output Wiring

Wiring specifications for the standard and optional alarm relays.

Extech VFL Controller Product Description

96VFL Front Panel Overview

Description of the front panel components and indicators for the 96VFL model.

48VFL Front Panel Overview

Description of the front panel components and indicators for the 48VFL model.

Keypad Functions

Explanation of the functions of each key on the controller's keypad.

Display Descriptions

Details on the Process Variable (PV) and Setpoint Variable (SV) displays.

Process Control Methods

Connecting Inputs

Guidance on connecting various input types to the controller.

Connecting Outputs

Guidance on connecting various output types from the controller.

Controller Programming

Overview of programming menus for optimizing process control.

Primary Relay Output Control

Explanation of the primary relay output's ON-OFF control capabilities.

Secondary Relay Output Control

Details on the secondary (optional) relay output and its control.

Pulsed DC Trigger Output

Information on the pulsed DC trigger output for ON-OFF control.

Analog Output Option

Explanation of the optional 4-20mA analog output for process control.

ON-OFF Control

Description of the basic ON-OFF control method and hysteresis.

PID Control Fundamentals

Explanation of PID control elements and its importance for precision.

PID Time Proportioning Control

Details on PID control for relay outputs using time proportioning.

Proportional Control Considerations

Discussion of Proportional Band (Pb) impact on controller reaction.

Dead-Band Considerations

Explanation of the dead band (db) parameter for output control.

Extech VFL Programming Menu Basics

Programming Menu 1: User Level

Programming Menu 2: Soft Start Level

Soft-Start Utility Overview

Overview of the soft-start utility to restrict output on start-up.

Ramp-to-Setpoint (RAMP) Overview

Explanation of the Ramp-to-Setpoint feature for controlling PV change rate.

Programming Menu 3: PID Tuning

Programming Menu 4: Options

Input Type Selection

Guide to selecting the correct input type for the controller's hardware.

Low and High Limit Considerations

Discussion on setting low and high limits for input ranges.

Alarm Function and Modes

Lists and descriptions of available alarm functions and modes.

ON-OFF Alarm Timers

Details on using alarm relays as ON or OFF timers for process stages.

RS-485 Interface Option

Information on the optional RS-485 PC communications utility.

Programming Menu 5: Linear Input

Automatic Tuning Procedure

Automatic and Manual Control Modes

Troubleshooting Common Errors

Heating Process Example

Extech VFL Controller Specifications

General Specifications

Overview of general technical specifications for the VFL series controllers.

Thermocouple Input Specifications

Detailed specifications for thermocouple input types.

RTD Input Specifications

Detailed specifications for RTD input types.

Analog Input Specifications

Detailed specifications for analog (linear) input types.

Relay and DC Trigger Output Specs

Specifications for relay and DC trigger control outputs.

Alarm Output Specifications

Specifications for alarm relay outputs and modes.

Analog Output Specifications

Specifications for the analog output (4-20mA).

Two-Year Product Warranty

Calibration and Repair Services

Customer Support Information