Rockwell Automation Allen-Bradley 700-SA User guide

Solid-State Relays
700-SA -SC, -SE, -SF, -SH, -SK
Application Guide

Important User Information
Because of the variety of uses for the products described in this
publication, those responsible for the application and use of this
control equipment must satisfy themselves that all necessary steps
have been taken to assure that each application and use meets all
performance and safety requirements, including any applicable laws,
regulations, codes and standards.
The illustrations, charts, sample programs and layout examples shown
in this guide are intended solely for purposes of example. Since there
are many variables and requirements associated with any particular
installation, Allen-Bradley does not assume responsibility or liability
(to include intellectual property liability) for actual use based upon
the examples shown in this publication.
Allen-Bradley publication SGI-1.1, Safety Guidelines for the
Application, Installation and Maintenance of Solid-State Control
(available from your local Allen-Bradley office), describes some
important differences between solid-state equipment and
electromechanical devices that should be taken into consideration
when applying products such as those described in this publication.
Reproduction of the contents of this copyrighted publication, in whole
or part, without written permission of Rockwell Automation, is
prohibited.
Throughout this manual we use notes to make you aware of safety
considerations:
Attention statements help you to:
•identify a hazard
•avoid a hazard
•recognize the consequences
Allen-Bradley is a trademark of Rockwell Automation
ATTENTION
!
Identifies information about practices or circumstances
that can lead to personal injury or death, property damage
or economic loss
IMPORTANT Identifies information that is critical for successful
application and understanding of the product.

European Communities (EC)
Directive Compliance
If this product has the CE mark it is approved for installation within
the European Union and EEA regions. It has been designed and
tested to meet the following directives.
EMC Directive
This product is tested to meet the Council Directive 89/336/EC
Electromagnetic Compatibility (EMC) by applying the following
standards, in whole or in part, documented in a technical
construction file:
•EN 61000-6-2 EMC — Generic Standards — Immunity for
Industrial Environments
This product is intended for use in an industrial environment.
Low Voltage Directive
This product is tested to meet Council Directive 73/23 EEC as
ammended by 93/68 EEC Low Voltage, by applying the safety
requirements of EN 60950 and safety requirements for “Safety of
Information Technology Equipment — General Requirements.”
This equipment is classified as open equipment and must be
mounted as instructed in an enclosure during operation to provide
safety protection.

Important User Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
European Communities (EC) Directive Compliance . . . . . . . . . . . . . iii
EMC Directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Low Voltage Directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Preface
Manual Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Who Should Use This Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Manual Explanation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
For Further Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Chapter 1 — Basic Concepts of SSRs
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
What are SSRs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Configuration of SSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
Representative Example of Switching
AC Loads for SSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1- 2
Electromagnetic Relay (EMR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 1- 3
Control of SSRs (ON/OFF Control, Cycle
Control, Phase Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
ON/OFF Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Cycle Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Phase Control (Single Phase) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
SSR Application Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
SSR Classifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Classification by Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
SSR Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9
Chapter 2 — Considerations When Designing SSR Control Systems
Input Circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Input Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Input Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
Output Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
AC ON/OFF SSR Output Noise Surges . . . . . . . . . . . . . . . . . . 2-5
DC ON/OFF Output Noise Surges . . . . . . . . . . . . . . . . . . . . . . 2-6
Self-Holding Latching Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
Selecting a SSR For Different Loads . . . . . . . . . . . . . . . . . . . . . . 2-7
Inrush Currents From Transformer Loads . . . . . . . . . . . . . . . . 2-11
Transformer Tap Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
Controlling Power for Transformer Loads . . . . . . . . . . . . . . . . 2-13
Load Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
Rectified Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
Operating Frequency for AC Load Power Supply . . . . . . . . . . 2-14
Low AC Voltage Loads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14
Phase-controlled AC Power Supplies. . . . . . . . . . . . . . . . . . . . . 2-14
Application Circuit Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-15
Connection to a Sensor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-15
Switching Control of an Incandescent Lamp . . . . . . . . . . . . . . 2-15
Temperature Control of an Electric Furnace. . . . . . . . . . . . . . . 2-15
Forward and Reverse Operation of a Single-phase Motor . . . . 2-15

ON/OFF Control of a Three-phase Inductive Motor . . . . . . . 2-16
Forward and Reverse Operation of a
Three-phase Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-16
Fail-safe Concept Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-17
Error Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-17
Short-circuit Protection (Fuse Selection) and
Overcurrent Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-18
SSR Operation Indicator (LED) . . . . . . . . . . . . . . . . . . . . . . . . . 2-19
Heat Radiation Design Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19
SSR Heat Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19
Heat Sink Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19
Calculating Heat Sink Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20
Designing for Control Panel Heat Radiation . . . . . . . . . . . . . . . 2-21
Chapter 3 — Mounting and Installation
Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Leakage Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Screw Tightening Torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
SSR Mounting Panel Quality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Panel/Surface-mounting Socket . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
SSR Insertion and Removal Direction . . . . . . . . . . . . . . . . . . . . . 3-2
Panel Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Relationship Between SSRs and Wire Ducts . . . . . . . . . . . . . . . . 3-3
Ventilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
Confirmation after Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
Operation and Storage Environment Precautions . . . . . . . . . . . . . . . 3-5
Ambient Temperature (Operating). . . . . . . . . . . . . . . . . . . . . . . . 3-5
Operation and Storage Locations . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Vibration and Shock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Oil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Handling the SSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Chapter 4 — Q and A
What Is Zero Cross Function? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Why Does the Input Current Vary With the SSR?. . . . . . . . . . . . . . . 4-2
What Is The Difference in Switching with a
Thyristor and a Triac? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
What Are the Characteristics of Thyristors and Triacs?. . . . . . . . . . . 4-3
What Is a Snubber Circuit? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
Are There Any SSRs With Normally Closed Contacts?. . . . . . . . . . . 4-4
What Is the Difference Between Recommended
Values and Rated Values? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
What Is Counter-electromotive Force?. . . . . . . . . . . . . . . . . . . . . . . . .4-5
What Is the Meaning of I2t for Fuse Selection?. . . . . . . . . . . . . . . . . 4-5
Why Does the Operating Time Vary Between AC Inputs
and DC Inputs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
What Is the Relationship Between the Leakage
Current and Load Voltage?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

Is It Possible to Connect SSRs In a Series? . . . . . . . . . . . . . . . . . . . . 4-6
Is It Possible to Connect Two 200V AC SSRs in
Series to a 400V AC Load? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
Is It Possible to Connect SSRs in Parallel?. . . . . . . . . . . . . . . . . . . . . 4-6
Is It Possible to Connect a DC Output Load to a Negative
Electrode? Can Either a Positive or Negative
Load Be Connected? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7
What Portion of the Power Factor of the Load
Is Practically Applicable?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7
Why Is the Minimum Load Current for Most SSRs
Limited to 0.1 A? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7
Why Can Most SSRs Not Switch Micro-loads? . . . . . . . . . . . . . . . . . 4-8
SSRs with AC Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4- 8
Why Does a Relay Make Noise When
Switched With a SSR?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4- 8
Why Is the Current Not Stable When the Power Supply Is
Switched ON and OFF? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9
How Much Thermal Resistance Is Required in the Heat Sink?
What Is the Thermal Resistance of the SSR? . . . . . . . . . . . . . . . . . . 4-10
Can A Panel Frame Be Used in Place of Heat Sink? . . . . . . . . . . . . 4-10
What Are the Carry Current Statistics of the Radiator?. . . . . . . . . . 4-11
Why Is It Necessary to Apply Grease to the SSR/Heat Sink? . . . . 4-11
Available Silicon Grease Products for Heat Dissipation. . . . . . 4-12
What Output Configuration Is Suitable
When the SSR Is Used in Combination
With a Temperature Controller? . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12
What Precautions Are Necessary When Driving a Number of SSRs
With a Temperature Controller Output? . . . . . . . . . . . . . . . . . . . . 4-12
Examples of Connections Between Temperature Controllers
and SSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13
What Precautions Are Necessary For Forward/Reverse
Operation of a Single-phase Motor?. . . . . . . . . . . . . . . . . . . . . . . . . 4-14
Precautions for Forward/Reverse Operation . . . . . . . . . . . . . . 4-14
Does an SSR Have a Mounting Direction? . . . . . . . . . . . . . . . . . . . 4-15
What Precautions Are Required For High-Density
Mounting or Gang Mounting? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16
What Is the Non-Repetitive Inrush Current?. . . . . . . . . . . . . . . . . . 4-16
What Kind of Failure Do SSRs Have Most Frequently?. . . . . . . . . 4-17
What Will Happen if the Load Voltage Eceeeds
the Upper Limit?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17
Is It Possible to Replace a Defective Part in a SSR? . . . . . . . . . . . . 4-18
How Can We Use a Multimeter to Check
If the SSR is ON or OFF? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18
Chapter Five — Troubleshooting Flowcharts . . . . . . . . . . . . . .5-1
Appendix
List of Recommended Loads . . . . . . . . . . . . . . . . . . . . . . . . Appendix-1
Circuit Configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix-2

5Publication 700-AT001A-EN-E June 2002
Preface
Manual Objectives
The purpose of this manual is to provide you with the additional information
necessary to apply Bulletin 700-S Solid-state Relays . Described in this manual
are methods for applying and troubleshooting this product.
Who Should Use This
Manual
This manual is intended for qualified personnel responsible for setting up and
servicing these devices. You must have previous experience with and a basic
understanding of wiring diagrams, configuration procedures, related
equipment, and safety precautions.
Manual Explanation
“SSR” stands for solid-state relay. First marketed in the 1970’s, SSRs have
become very popular for the following reasons:
•They provide a means of creating no-contact relays in output power sections
enabling conversion of control circuits to ICs.
•They provide a means of increasing the service life of the application and
reducing maintenance time and costs.
•They provide a means of preventing operating errors caused through noise by
isolating signal circuits and outputs.
•They provide a means of eliminating the clicking sounds produced when
mechanical relay load currents turn ON.
In these and other ways, SSRs have proven to provide many special
characteristics to meet market needs.
This manual has been produced in response to demand from customers to
provide the product and technical information required to select the best SSRs
according to purpose and application.
For Further Information
Relays and Timers Selection Guide
•Publication 700-SG003B-EN-P

1-1 Publication 700-AT001A-EN-E June 2002
Chapter
1
Basic Concepts of SSRs
Overview
What are SSRs?
Difference between SSRs and Mechanical Relays
SSRs (solid-state relays) have no movable contacts. SSRs are not very different in
general operation from mechanical relays that have movable contacts. SSRs,
however, employ semiconductor switching elements, such as thyristors, triacs,
diodes, and transistors. Furthermore, SSRs employ optical semiconductors called
photocouplers to isolate input (control) and output (load) signals. Photocouplers
change electric signals into optical signals and transmit the signals through space,
thus fully isolating the input and output sections while transferring the signals at
high speed.
SSRs consist of electronic parts with no mechanical contacts. Therefore,
SSRs have a variety of features that mechanical relays do not
incorporate. The greatest feature of SSRs is that SSRs do not use
switching contacts that will physically wear out.
SSRs are ideal for a wide range of applications due to the following
performance characteristics:
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Publication 700-AT001A-EN-E June 2002
1-2 Basic Concepts of SSRs
Configuration of SSRs
Representative Example of Switching AC Loads
Isolated input circuit
Input
terminals
Input circuit
Electrical isolation
Drive circuit
Output circuit
Output
terminals
SSR circuit
configuration
Semiconductor
output element
Input
terminals
and transistor Diode, LED, resistor,
Phototriac coupler Photocoupler
Diode, capacitor, resistor, and varistor
Resistor, capacitor, and varistor
power transistor, thyristor,
Output
terminals
SSR
Component
Configuration
Power transistor (for DC loads)
Thyristor (for AC loads)
Triac (for AC loads)
and triac
Input Output
Light
Phototriac
coupler Triac
No
operation
noise
Long
life SSRs are
SPST-NO
Input circuit
Zero cross function
Trigger circuit
High-speed,
high-frequency
switching
Minimal
noise
generation
Heat
dissipation
is required
A surge
voltage
may
damage
the
elements.
Leakage
current
Drive
circuit Snubber
circuit

Publication 700-AT001A-EN-E June 2002
Basic Concepts of SSRs 1-3
Electromagnetic Relay (EMR)
An EMR generates electromagnetic force when input voltage is
applied to the coil. The electromagnetic force moves the armature that
switches the contacts in synchronization. EMRs are used for a wide
range of applications. The principle of the operation of EMRs is simple
and it is possible to manufacture EMRs at low costs.
Control of SSRs (ON/OFF Control)
ON/OFF control is a form of control where a device such as a heater
is turned ON or OFF by turning a SSR ON or OFF in response to
voltage output signals from a Temperature Controller. The same kind
of control is also possible with an electromagnetic relay but if the
heater is turned ON and OFF at intervals of a few seconds
(high-frequency switching) over a period of several years, then an SSR
must be used.
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Publication 700-AT001A-EN-E June 2002
1-4 Basic Concepts of SSRs
ON/OFF Control
SSR Application Examples
SSRs are used for a variety of electric machines and devices
SSR Classifications
SSRs can be classified by appearance, such as panel-mounting models,
socket models, or by applications, as shown below. The optimum SSR
can be selected depending on the purpose.
ON OFF
2 s
SSR
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Publication 700-AT001A-EN-E June 2002
Basic Concepts of SSRs 1-5
Applications
Industrial machinery
Physics and chemistry
Automatic vending
and amusement
Transportation
Factory machines (e.g., molding machines)
Food-related machines (e.g., packaging machines)
Industrial robots
Industrial machines and control equipment
(e.g., programmable controllers)
Medical equipment (e.g., CT scanners)
Physical and chemical equipment
(e.g., temperature controlled baths)
Automatic vending machines
Amusement machines
Railroad-related applications (e.g., lamp and seat heaters)
Traffic signals

Publication 700-AT001A-EN-E June 2002
1-6 Basic Concepts of SSRs
Classification by Application
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Heater Control
These SSRs are applicable to machines
which require highly sensitive temperature
control for turning heaters ON and OFF, such
as molding equipment, packaging machines,
and solderers. They meet the high-capacity,
high ON/OFF frequency requirements of
heater control.
Motor Control
These SSRs are applicable to machines
which require motor inching operation and
reversible operation, such as machine tools,
conveyors, and packaging equipment. They
have high-speed response time and high
ON/OFF frequency, required for inching and
reversible operation.
I/O
These SSRs meet the requirements for
isolated transmission of control output from
PCs and Position Controllers to an actuator.
Amusement Machines
These SSRs have high ON/OFF frequency,
noiseless operation, and when compared to
mechanical relays, have greater resistance to
vibration, shock, dust and dirt, and gas,
making them ideal for situations where these
factors are important.
Panel-mounted Interfaces
These SSRs are the same shape as
general-purpose relays, they have the same
sockets and can be mounted according to
their respective shapes.
They are ideal for interface applications
where high-frequency switching is required,
and can also be used in a wide variety of
general-purpose applications, such as
directly switching loads.
700-SH 700-SE
700-SH 700-SE
700-SK
700-SH
700-SA 700-SC 700-SF 700-SK

Publication 700-AT001A-EN-E June 2002
Basic Concepts of SSRs 1-7
SSR Glossary
Terms Meaning
Insulation Basic insulation Insulation for basic protection from electric shock
(IEC950 1.2.9.2)
Supplemental
insulation Independent insulation provided outside of basic insulation to protect from electric shock when the
basic insulation breaks down (IEC950 1.2.9.3)
Reinforced
insulation A single-layer of insulation (IEC950 1.2.9.5) that provides the same protection from electric shock as
double insulation (insulation including both basic and
supplemental insulation) according to conditions
stipulated in IEC950 standards
Circuit
functions Zero cross circuit A circuit which starts operation with the AC load voltage at close to zero-phase.
Trigger circuit A circuit for controlling the triac or thyristor trigger
signal, which turns the load current ON and OFF.
Input Isolated input
circuit If the external circuit is prone to generating noise, or if wires from external sources are prone to the
influence of inductive noise, in order to prevent
malfunctions due to noise, it is necessary to
electrically isolate internal circuits and external
circuits (output circuits). An isolated input circuit is a
circuit that isolates inputs and outputs by using
components that are not connected electrically but
that can transmit signals, such as contact relays or
photocouplers.
Photocoupler A component that runs the electric signal into a light
emitter (e.g., LED), changes it to a light signal, and
then returns it to an electric signal using a
photoelectric conversion element, such as a photo
transistor. The space used for transferring the light
signal is isolated thus providing good insulation and
a high propagation speed.
Rated voltage The voltage that serves as the standard value of an
input signal voltage
Must-operate
voltage Minimum input voltage when the output status changes from OFF to ON.
Input impedance The impedance of the input circuit and the resistance
of current-limiting resistors used. Impedance varies
with the input signal voltage in case of the constant
current input method.
Operating
voltage The permissible voltage range within which the voltage of an input signal voltage may fluctuate.
Reset voltage Maximum input voltage when the output status
changes from ON to OFF.
Input current The current value when the rated voltage is applied.

Publication 700-AT001A-EN-E June 2002
1-8 Basic Concepts of SSRs
Output Load voltage This is the effective value for the power supply
voltage that can be used for load switching or in the
continuous-OFF state.
Maximum load
current
(continuous)
The effective value of the maximum current that can
continuously flow into the output terminals under
specified cooling conditions (i.e., the size, materials,
thickness of the heat sink, and an ambient
temperature radiating condition).
Output Leakage
current The effective value of the current that can flow into the output terminals when a specified load voltage is
applied to the SSR with the output turned OFF.
Output ON
voltage drop The effective value of the AC voltage that appears across the output terminals when the maximum load
current flows through the SSR under specified
cooling conditions (such as the size, material, and
thickness of heat sink, ambient temperature
radiation conditions, etc.).
Minimum load
current The minimum load current at which the SSR can operate normally.
Snubber circuit A circuit consisting of a resistor R and capacitor C,
which prevents faulty ignition from occurring in the
SSR triac by suppressing a sudden rise in the voltage
applied to the triac.
Semiconductor
output element
(load switching
device)
This is a generic name for semiconductors such as
the thyristor, triac, and power transistor. In
particular, triacs are often used in SSRs because they
allow switching to be performed with one element.
Repetitive peak
OFF-state
voltage (VDRM)
This is a rating for an output semiconductor that is
used in a SSR for AC loads.
Collector-emitter
voltage (VCEO) This is a rating for an output semiconductor that is used in an SSR for DC loads.
Characteristics Operating time
(pick-up time) A time lag between the moment a specified signal voltage is imposed to the input terminals and the
output is turned ON.
Release time
(drop-out time) A time lag between the moment the imposed signal input is turned OFF and the output is turned OFF.
Insulation
resistance The resistance between the input and output terminals or I/O terminals and metal housing (heat
sink) when DC voltage is imposed.
Dielectric
strength The effective AC voltage that the SSR can withstand when it is applied between the input terminals and
output terminals or I/O terminals and metal housing
(heat sink) for more than 1 minute.
Ambient
temperature and
humidity
(operating)
The ranges of temperature and humidity in which the
SSR can operate normally under specified cooling,
input/output voltage, and current conditions.
Storage
temperature The temperature range in which the SSR can be stored without voltage imposition.
Terms Meaning

Publication 700-AT001A-EN-E June 2002
Basic Concepts of SSRs 1-9
Others Inrush current A current which can be applied for short periods of
time to the electrical element.
Counter-electro
motive force Extremely steep voltage rise which occurs when the load switched or turned OFF.
Recommended
applicable load The recommended load capacity which takes into account the safety factors of ambient temperature
and inrush current.
Bleeder
resistance The resistance connected in parallel to the load in order to increase apparently small load currents, so
that the ON/OFF of minute currents functions
normally. (It is also used to shunt leakage currents.)
Terms Meaning

2-1 Publication 700-AT001A-EN-E June 2002
Chapter
2
Considerations When Designing SSR Control
Systems
Input Circuit
Input Noise
SSRs need only a small amount of input/control power to operate. This
is why the input terminals must shut out electrical noise as much as
possible. Noise applied to the input terminals may result in malfunction.
The following describe measures to be taken against electrical pulse
noise and inductive noise.
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A combination of capacitor and resistor on the input/control circuit can
absorb pulse noise effectively. The following is an example of a noise
absorption circuit with capacitor C and resistor R connected to an SSR.
The value of R and C must be decided carefully. The value of R must
not be too large or the supply voltage (E) will not be able to satisfy the
SSR’s required input must operate (ON) voltage value. The larger the
value of C, the longer the release time will be, due to the time required
for C to discharge electricity.
Pulse width
Pulse voltage
R
C
E

Publication 700-AT001A-EN-E June 2002
2-2 Considerations When Designing SSR Control Systems
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Do not wire high voltage power lines alongside the low voltage SSR
input/control lines. Inductive noise may cause the SSR to malfunction,
turn off unexpectedly, or both. If inductive noise is imposed on the
input terminals of the SSR, use the following cables according to the
type of inductive noise, to help reduce the noise level to less than the
reset voltage of the SSR:
Twisted-pair wires: For electromagnetic noise
Shielded cable: For static noise
A filter consisting of a combination of capacitor and resistor will
effectively reduce noise generated from high-frequency equipment.
Note: R: 20…100 Ω
C: 0.01… 1 µF
Pulse voltage (V)
Pulse width ( s)
µ
0.01 µF
Filter
High-frequency
device
Load

Publication 700-AT001A-EN-E June 2002
Considerations When Designing SSR Control Systems 2-3
Input Conditions
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When there is a ripple in the input control voltage, ensure that the
peak voltage of the ripple is lower than the maximum operating SSR
voltage and the root voltage is above the SSR minimum operating
voltage.
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When the SSR input circuit is powered by a transistor output, the SSR
reset voltage may be insufficient due to leakage current of the
transistor during power OFF. To counteract this, connect a bleeder
resistance R as shown in the diagram below and set the resistance so
that the voltage applied to both ends of the resistance is less than half
of the reset voltage of the SSR.
The bleeder resistance R can be obtained in the way shown below.
E: Voltage applied at both ends of the bleeder resistance = half of the
reset voltage of the SSR
IL: Leakage current of the transistor
I: Reset current of the SSR
The actual value of the reset current is not given in the datasheet and
so when calculating the value of the bleeder resistance, use the
following formula:
Peak voltage
Root voltage
0 V
Bleeder resistance
R
5(
,/−,
≤
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Publication 700-AT001A-EN-E June 2002
2-4 Considerations When Designing SSR Control Systems
For SSRs with constant-current input circuits (e.g., 700-SH) calculation
is performed at 0.1 mA.
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The ON/OFF frequency should be set to 10 Hz maximum for an AC
load and 100 Hz maximum for DC load ON/OFF. If ON/OFF occurs
at frequencies exceeding these values, the SSR output will not be able
to follow up.
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In SSRs that have a wide input voltage range (such as 700-SC and
700-SF), the input impedance varies according to the input voltage
and changes in the input current. If the input voltage is low, the
influence of the voltage drop for the input LED is large, and the input
impedance will be higher than expected. If the voltage is so high that
the LED voltage drop can be ignored, the input impedance will be
close to the resistance R.
For semiconductor-driven SSRs, changes in voltage can cause
malfunction of the semiconductor, so be sure to check the actual
device before usage. See the following examples. Refer to the SSR’s
datasheet for the impedance of individual SSR models.
Input
R = 2 kΩ
R = 1.5 kΩ
Applicable Input Impedance for a Photocoupler-type SSR
without Indicators (Example)
700-SC (Without Indicators)
Input current (mA)
Input impedance (k )
Ω
Input voltage (V)
Input current
Input impedance