Technical Guide

Control Components

Timers

Counters

Cam Positioners

Temperature Controllers

Digital Panel Indicators

Temperature Controller / Temperature Sensor Glossary

Glossary of Control Terminology

Hysteresis

ON/OFF control action turns the output ON or OFF based on the set point. The output frequently changes according to minute temperature changes as a result, and this shortens the life of the output relay or unfavorably affects some devices connected to the Temperature Controller. To prevent this from happening, a temperature band called hysteresis is created between the ON and OFF operations.

Hysteresis (Reverse Operation)

Example:

If a Temperature Controller with a temperature range of 0 to 400 °C has a 0.2% hysteresis, D will be 0.8 °C. If the set point is 100 °C, the output will turn OFF at a process value of 100 °C and will turn ON at a process value of 99.2 °C.

Hysteresis (Forward Operation)

Example:

If a Temperature Controller with a temperature range of 0 to 400 °C has a 0.2% hysteresis, D will be 0.8 °C. If the set point is 100 °C, the output will turn OFF at a process value of 100 °C and will turn ON at a process value of 100.8 °C.

Offset

Proportional control action causes an error in the process value due to the heat capacity of the controlled object and the capacity of the heater. The result is a small discrepancy between the process value and the set point in stable operation. This error is called offset. offset is the difference in temperature between the set point and the actual process temperature. It may exist above or below the set point.

Hunting and Overshooting

ON/OFF control action often involves the waveform shown in the following diagram. A temperature rise that exceeds the set point after temperature control starts is called overshooting. Temperature oscillation near the set point is called hunting. Improved temperature control is to be expected if the degree of overshooting and hunting are low.

Hunting and Overshooting in ON/OFF Control Action

Control Cycle and Time-Proportioning Control Action

The control output will be turned ON intermittently according to a preset cycle if P action is used with a relay or SSR. This preset cycle is called the control cycle and this method of control is called time-proportioning control action.

Example:

If the control cycle is 10 s with an 80% control output, the ON and OFF periods will be as follows.

Derivative Time

Derivative time is the period required for a ramp-type deviation in derivative control (e.g., the deviation shown in the following graph) that coincides with the control output in proportional control action. The longer the Derivative time is the stronger the derivative control action will be.

PD Action and Derivative Time

Integral Time

Integral time is the period required for a step-type deviation in integral control (e.g., the deviation shown in the following graph) to coincide with the control output in proportional control action. The shorter the Integral time is the stronger the integral action will be. If the Integral time is too short, however, hunting may result.

PI Action and Integral Time

Constant Value Control

For constant value control, control is preformed at specific temperatures.

Program Control

Program control is used to control temperature for a target value that
changes at predetermined time intervals.

Auto-tuning

The PID constant values and combinations that are used for temperature control depend on the characteristics of the controlled object. A variety of conventional methods that are used to obtain these PID constants have been suggested and implemented based on actual control temperature waveforms. Auto-tuning methods make it possible to obtain PID constants suitable to a variety of controlling objects. The most common types of Auto-tuning are the step response, marginal sensitivity, and limit cycle methods.

Step Response Method

The value most frequently used must be the set point in this method. Calculate the maximum temperature ramp R and the dead time L from a 100% step-type control output. Then obtain the PID constants from R and L.

Marginal Sensitivity Method

Proportional control action begins from start point A in this method. Narrow the width of the proportional band until the temperature starts to oscillate. Then obtain the PID constants from the value of the proportional band and the oscillation cycle time T at that time.

Limit Cycle Method

ON/OFF control begins from start point A in this method. Then obtain the PID constants from the hunting cycle T and oscillation D.

Readjusting PID Constants

PID constants calculated in auto-tuning operation normally do not cause problems except for some particular applications. In those cases, refer to the following diagrams to readjust the constants.

Response to Change in the Proportional Band

Wider

It is possible to suppress overshooting although a comparatively long startup time and set time will be required.

Narrower

The process value reaches the set point within a comparatively short time and keeps the temperature stable although overshooting and hunting will result until the temperature becomes stable.

Response to Change in Integral Time

Wider

The set point takes longer to reach. It is possible to reduce hunting, overshooting, and undershooting although a comparatively long startup time and set time will be required.

Narrower

The process temperature reaches the set point within a comparatively short time although overshooting, undershooting, and hunting will result.

Response to Change in Derivative Time

Wider

The process value reaches the set point within a comparatively short time with comparatively small amounts of overshooting and undershooting. Fine-cycle hunting will result due to the change in process value.

Narrower

The process value will take a relatively long time to reach the set point with heavy overshooting and undershooting.

Fuzzy Self-tuning

PID constants must be determined according to the characteristics of the controlled object for proper temperature control. The conventional Temperature Controller incorporates an auto-tuning function to calculate PID constants. In that case, it is necessary to give instructions to the Temperature Controller to trigger the auto-tuning function. Furthermore, temperature disturbances may result if the limit cycle is adopted. The Temperature Controller in fuzzy self-tuning operation determines the start of tuning and ensures smooth tuning without disturbing temperature control. In other words, the fuzzy self-tuning function makes it possible to adjust PID constants according to the characteristics of the controlled object.

Fuzzy Self-tuning in 3 Modes

• PID constants are calculated by tuning when the set point changes.

• When an external disturbance affects the process value, the PID constants will be adjusted and kept in a specified range.

• If hunting results, the PID constants will be adjusted to suppress hunting.

Auto-tuning with a Conventional Temperature Controller

Auto-tuning (AT) Function:
A function that automatically calculates optimum PID constants for controlled objects.

Features:
(1) Tuning will be performed when the AT instruction is given.
(2) The limit cycle signal is generated to oscillate the temperature before tuning.

Self-tuning

Self-tuning (ST) Function:
A function that automatically calculates optimum PID constants for controlled objects.

Features:
(1) Whether to perform tuning or not is determined by the Temperature Controller.
(2) No signal that disturbs the process value is generated.

Self-tuning is supported by most of OMRON temperature controllers. Trends in temperature changes are used to automatically calculate and set a suitable proportional band.

PID Control and Tuning Methods for Temperature Controllers

ST: Fuzzy self-tuning, ST**: Executed only for SP changes, AT: Auto-tuning
Note: Not including the E5ZN

Control Outputs

Relay output:
Contact relay output used for control methods with comparatively low switching frequencies.

SSR output:
Non-contact solid-state relay output for switching 1 A maximum.

Voltage output (ON/OFF output):
ON/OFF pulse output at 5, 12, or 24 VDC externally connected to a high-capacity SSR. ON/OFF action is ideal for high switching frequency and PID action is ideal for time-proportioning control action.

Current output:
Continuous 4- to 20-mA or 0- to 20-mA DC output used for driving power controllers and electromagnetic valves. Ideal for high-precision control. A preset linear output is produced if the load resistance falls below allowable levels.

Voltage output (Linear output):
Continuous 0 to 5 or 0 to 10 VDC output used for driving pressure controllers. Ideal for high-precision control.

Glossary of Alarm Terminology

Alarm Operation

The Temperature Controller compares the process value and the preset alarm value, turns the alarm signal ON, and displays the type of alarm in the preset operation mode.

Deviation Alarm

The deviation alarm turns ON according to the deviation from the set point in the Temperature Controller.

Setting Example

Alarm temperature is set to 110°C.
The alarm set point is set to 10°C.

Absolute-value Alarm

The absolute-value alarm turns ON according to the alarm temperature regardless of the set point in the Temperature Controller.

Setting Example

Alarm temperature is set to 110°C.
The alarm set point is set to 110°C.

Standby Sequence Alarm

It may be difficult to keep the process value outside the specified alarm range in some cases (e.g., when starting up the Temperature Controller), and the alarm turns ON abruptly as a result. This can be prevented with the standby sequential function of the Temperature Controller. This function makes it possible to ignore the process value right after the Temperature Controller is turned ON or right after the Temperature Controller starts temperature control. In this case, the alarm will turn ON if the process value enters the alarm range after the process value has been once stabilized.

Example of Alarm Output with Standby Sequence Set

Temperature Rise

Temperature Drop

SSR Failure Alarm

(Applicable models: E5CN)

The SSR Failure Alarm is output when an SSR short-circuit failure is detected. A ct (Current Transformer) is used by the Temperature Controller to detect heater current and it outputs an alarm when a short circuit occurs.

Heater Burnout Alarm

(Three phase (E5CN, E5AN, and E5EN only) and single phase)

Many types of heaters are used to raise the temperature of the controlled object. The ct (Current Transformer) is used by the Temperature Controller to detect the heater current. If the heater's power consumption drops, the Temperature Controller will detect heater burnout from the ct and will output the heater burnout alarm.

Alarm Latch

The alarm will turn OFF if the process value falls outside alarm operation range. This can be prevented if the process value enters the alarm range and an alarm is output by holding the alarm output until the power supply turns OFF.

LBA (Operates differently in the E5[]K and E5CN)

(Applicable models: E5[]K)
The LBA (loop break alarm) is a function that turns the alarm signal ON by assuming the occurrence of control loop failure if there is no input change with the control output set to the highest or lowest value. Therefore, this function can be used to detect control loop errors.

(Applicable models: E5CN, E5AN, and E5EN)
The LBA (loop break alarm) is a function that turns the alarm signal ON by assuming the occurrence of control loop failure if there is no input change with the deviation above a certain level. Therefore, this function can be used to detect control loop errors.

Configurable Upper and Lower Limit Alarm Settings

(Applicable models: E5[]N and E5[]R)

Glossary of Temperature Sensor Terminology

Cold Junction Compensating Circuit

The thermo-electromotive force of the thermocouple is generated according to the temperature difference between the hot and cold junctions. If the cold junction temperature fluctuates, the measurement data will fluctuate even if the hot junction temperature remains stable. For this reason, a separate sensor built into the controller is used to monitor any changes in the cold junction (terminal connected to the thermocouple), and the controller automatically compensates for these changes to keep the cold end of the device at 0°C. This is called cold junction compensation.

The thermoelectromotive force V_T is calculated from the following formula: V_T = V (350 − 20)

Compensating Conductor

An actual application may have a sensing point located far away from the Temperature Controller. Compensating conductors are connected to the thermocouple in this case because thermocouple conductors are expensive. The Compensating conductor must conform to the characteristics of the thermocouple, otherwise precise temperature sensing will not be possible.

Example of Compensating Conductor Use

Input Shift

A preset point is added to or subtracted from the temperature detected by the Temperature Sensor of the Temperature Controller to display the process value. The difference between the detected temperature and the displayed temperature is set as an input compensation value.

Glossary of Output Terminology

Reverse Operation (Heating)

The Temperature Controller in reverse operation will increase control output if the process value is lower than the set point (i.e., if the Temperature Controller has a negative deviation).

Direct Operation (Cooling)

Heating and Cooling Control

Temperature control over a controlled object would be difficult if heating was the only type of control available, so cooling control was also added. Two control outputs (one for heating and one for cooling) can be provided by one Temperature Controller.

MV (Manipulated Variable) Limiter

The upper and lower limits for the MV limiter are set by the upper MV and lower MV settings. When the MV calculated by the Temperature Controller falls outside the MV limiter range, the actual output will be either the upper or lower MV limit.

With heating and cooling control, the cooling MV is treated as a negative value. Generally speaking then, the upper limit (positive value) is set to the heating output and the lower limit (negative value) is set to the cooling output as shown in the following diagram.

Rate of Change Limit

The rate of change limit for the MV sets the amount of change that occurs per second in the MV. If the MV calculated by the Temperature Controller changes significantly, the actual output follows the rate of change limiter setting for MV until it approaches the calculated value.

Dead Band

The overlap band and dead band are set for the cooling output. A negative value here produces an overlap band and a positive value produces a dead band.

Cooling Coefficient

When adequate control characteristics cannot be obtained using the same PID constants, such as when the heating and cooling characteristics of the controlled object vary significantly, adjust the proportional band on the cooling side (cooling side P) using the cooling coefficient until heating and cooling side control are balanced. P on the heating and cooling control sides is calculated from the following formula.

Heating side P = P
Cooling side P = Heating side P × cooling coefficient
For cooling side P control when heating side characteristics are different, multiply the heating side P by the cooling coefficient.

Heating Side P × 0.8

Heating Side P × 1.5

Positioning-Proportioning Control

This is also called ON/OFF servo control. When a Control Motor or Modutrol Motor with a valve is used in this control system, a potentiometer for open / closed control reads the degree of penning (position) of the control valve, outputs an open and close signal, and transmits the control output to Temperature Controller. The Temperature Controller outputs two signals: an open and close signal.

OMRON uses floating control. This means that the potentiometer does not feed back the control valve position and temperature can be controlled with or without a potentiometer.

Transfer Output

A Temperature Controller with current output independent from control output is available. The process value or set point within the available temperature range of the Temperature Controller is converted into 4- to 20-mA linear output that can be input into recorders to keep the results of temperature control on record. The transfer output will be turned ON between the upper and lower limits if the E5[]K-[]F the Temperature Controller is used.

Glossary of Setting Terminology

Set Limit

The set point range depends on the Temperature Sensor and the set limit is used to restrict the set point range. This restriction affects the transfer output of the Temperature Controller.

Multiple Set Points

Two or more set points independent from each other can be set in the Temperature Controller in control operation.

Setting Memory Banks

The Temperature Controller stores a maximum of eight groups of data (e.g., set value and PID constant data) in built-in memory banks for temperature control. The Temperature Controller selects one of these banks in actual control operation.

Set Point (SP) Ramp

The SP ramp function controls the target value change rate with the variation factor. Therefore, when the SP ramp function is enabled, some range of the target value will be controlled if the change rate exceeds the variation factor as shown on the right.

Remote Set Point (SP) Input

For a set point input - Glossary of Industrial Automation">remote set point input, the Temperature Controller uses an external input ranging from 4- to 20-mA for the target temperature. When the SP - Glossary of Industrial Automation">remote SP function is enabled, the 4- to 20-mA input becomes the remote set point.

Event Input

An event input is an external signal that can be used to control various actions, such as target value switching, equipment or process RUN/STOP, and pattern selection.

Input Digital Filter

The input digital filter parameter is used to set the time constant of the digital filter. Data that has passed through the digital filter appears as shown in the following diagram.

Temperature Sensor Glossary

Temperature Sensor Types and Features

Pt100 and JPt100

In January 1, 1989, the JIS standard for platinum resistance thermometers (Pt100) was revised to incorporate the IEC (International Electrotechnical Commission) standard. The new JIS standard was established on April 1, 1989. Platinum resistance thermometers prior to the JIS standard revision are distinguished as JPt100.Therefore, make sure that the correct resistance thermometer - Glossary of Industrial Automation">platinum resistance thermometer is being used.

The following table shows the differences in appearance of the Pt100 and JPt100.

Note: OMRON discontinued production of JPt100 Sensors in March of 2003.

Indicated Temperature when Connecting Pt100 Sensor to JPt100 Input

Indicated Temperature when Connecting JPt100 Sensor to Pt100 Input

Temperature Sensor Construction

Thermocouple Measuring Junction Construction

Terminal Block Appearance

	Exposed lead wires	Exposed terminals	Enclosed terminals
Features	Lead wires directly extend from protective tubing, enabling low-cost manufacturing without requiring more space. → For building into machines	Construction uses exposed terminal screws for easy maintenance. → For general-purpose indoor use	Construction with enclosed terminal screws enables broad range of applications. → For indoor industrial equipment
Appearance
Permissible temperature in dry air	• Sleeve Standard: 0 to +70°C Heat Resistive: 0 to +100°C • Lead wire (platinum resistance thermometer) Standard (vinyl-covered): −20 to +70°C Heat resistive (glass-wool-covered with stainless-steel external shield): 0 to 180°C • Lead wire (compensating conductor) Standard (vinyl-covered): −20 to +70°C Heat resistive (glass-wool-covered with stainless-steel external shield): 0 to 150°C	• Permissible temperature in dry air for terminal box: 0 to +100°C	• Permissible temperature in dry air for terminal box: 0 to +80°C

Temperature Sensor Thermal Response

A delay will occur before the temperature sensor reaches the temperature of the sensing object. This delay is generally referred to as the response time. JIS standards specify the response characteristics of a temperature sensor as the time required by the sensor to reach 63.2% of the indicated value for the temperature of the sensing object starting from when the temperature sensor touches the sensing object. Refer to the test results provided in the tables on the right.

Thermal Response of Sheathed Temperature Sensors

Protective tubing: SUS316

Standard Temperature Sensors
Thermal Response of Standard Thermocouple
 

Protective tubing: SUS316

Thermal Response of Platinum Resistance Thermometer
 

Protective tubing: SUS316

Vibration and Shock Resistance

The testing standards for temperature sensors specified by JIS are provided in the tables on the right. Refer to these standards and provide sufficient margins for the application conditions.

Vibration Resistance

Thermocouple

(Conforms to JIS C1602-1995)

Note: This test is not performed for Sensors with non-metal protective tubing. Fixed frequency durability tests are conducted at 70 Hz when the resonance point is 100 Hz.

Platinum Resistance Thermometer

(Conforms to JIS C1604-1997)

Shock Resistance

Holding the test product on its side, the product is then dropped from a height of 250 mm onto a steel plate 6 mm thick placed on a hard floor. This process is repeated 10 times, after which the product is checked for electrical faults in the measuring junctions and terminal contacts. This test is not performed, however, on products with non-metal protective tubing (conforms to JIS C1602-1995 and JIS C1604-1997).

Permissible Temperature in Dry Air

The permissible temperature in dry air refers to the temperature under which the thermoelectromotive force does not change above the values indicated in the following table when used continuously in static dry air for the time indicated in the following table. The permissible temperature depends on the type of lead wire (thermocouple), protective tubing material, and diameter. The life of thermocouples will generally be extended by lowering the operating temperature. Therefore, use the temperature sensors in conditions that provide sufficient margin in operating temperature beyond the permissible temperature in dry air.

(Conforms to JIS C1602-1995)

Sheathed

Thermocouple Permissible Temperature in Dry Air

M: Protective tubing material
D: Protective tubing diameter (mm)

Standard

Thermocouple Permissible Temperature in Dry Air

M: Protective tubing material
D: Protective tubing diameter (mm)

Permissible Temperature in Dry Air

Reference Material for Temperature Sensors

Thermocouple Standard Potential Difference

Thermocouples generate voltage according to the temperature difference. The potential difference is prescribed by Japanese Industrial Standards (JIS). The following chart gives the potential difference for R, S, K, and J thermocouples when the temperature of the reference junction is 0 °C.E5[]N, E5ZN, and E5[]R conform to standards published in 1995. Other Temperature Controllers conform to standards published in 1981 (listed below).

(Standards Published in 1995)

JIS C 1602-1995 (Unit: μV)

(Standards Published in 1981)

JIS C 1602-1981 (Unit: μV)

Reference Temperature Characteristics for Platinum Resistance Thermometers (Ω)

E5[]N, E5ZN, and E5[]R conform to JIS C 1604-1997. Other Temperature Controllers conform to JIS C 1604-1989.

Pt100

JIS C 1604-1997

JPt100

JIS C 1604-1997

Pt100

JIS C 1604-1989

JPt100

JIS C 1604-1989

Standard Temperature Characteristics for Element-interchangeable Thermistors

The following chart gives the temperature characteristics for low-cost thermistors used in the E5C2, E5L, and E5CS.

JIS C 1611-1975

Note: Amount of change in resistance per degree C in the resistance deviation and specified temperature.

Usage Limit for Bare Thermocouples (in Dry Air)
 

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