Toshiba Applications of photorelays to FA equipment Application Notes
Applications of photorelays to FA equipment
Application Notes
Applications of photorelays to FA equipment
Overview
Compared with mechanical relays, photorelays are superior in terms of long life, low current
drive, and high-speed response of contacts, and are increasingly being installed in FA equipment.
This document introduces examples of photorelay applications in FA equipment and describes
precautions when using photorelays.
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Toshiba Electronic Devices & Storage Corporation
Applications of photorelays to FA equipment
Application Notes
Table of cntents
Introduction ............................................................................................. 3
1.
2. Output Terminals (I/O), Alarm output applications ......................................... 4
2.1 Types of output terminals ........................................................................ 5
2.2 Application example of photorelay to transistor output terminal .................... 5
2.3 Example of photorelay application to contact output (mechanical relay) ........ 8
3. Analog measurement applications ............................................................. 11
3.1 Switching between Current and Voltage Measurements (Shunt Resistor) ..... 12
3.2 Gain control ......................................................................................... 12
3.3 Switching various sensor signals and eliminating mutual effects (noise) ....... 12
4. Conclusion ................................................................................................ 15
Revision History .............................................................................................. 16
RESTRICTIONS ON PRODUCT USE ..................................................................... 17
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Toshiba Electronic Devices & Storage Corporation
Applications of photorelays to FA equipment
Application Notes
1. Introduction
FA equipment used in various production sites and processes is evolving to meet a variety
of needs, including improved facility availability and production efficiency, higher precision,
improved safety, and energy conservation.
Specifically, in order to rationalize preventative maintenance from monitoring and
analysis of operating conditions, and to respond to predictive maintenance, we are
improving functions such as strengthened coordination between instrumentation and
control and equipment, and maintenance-free.
This application note introduces the case of output terminals for equipment I/O and the
case of analog signal measurement functions as examples of photorelay applications that
contribute to the improvement of these functions.
A brief introduction to the photorelay is given in front of this manual.
Photorelay is a type of solid-state relay that uses MOSFET for its contacts (switches). It is
also known as a photo-MOS relay or a MOSFET relay.
A photorelay consists of an LED that converts an electrical signal for controlling a contact
into an optical signal, a photodiode array (hereinafter referred to as PDA) that converts an
optical signal into an electrical signal, and a MOSFET that performs a contact function.
The operation of the photorelay is as follows (Fig. 1):
(1) To drive the contacts, apply current to the LEDs. The LED emits light and an optical
signal is generated.
(2) The optical signal is converted into an electric signal by the PDA on the contact side,
and an electric signal is input to the control terminals (gates) of MOSFETs.
(3) When an electric signal is input to the gate, MOSFETs turns ON and the contact is
connected.
Since the contact part is a semiconductor element, there is no mechanical wear, and even
if it is opened and closed repeatedly, there is no deterioration of the contact.
In order to obtain the electromagnetic force to move the contact, the mechanical relay
requires that a current of about tens of mA flow through the control coil.
In contrast, photorelays can operate MOSFETs with LED currents as small as a few
milliamperes. Therefore, it has features of long life, low drive input and high-speed
response compared with conventional mechanical relays.
Semiconductor relays use triacs with similar features, but photorelay with MOSFET has
the advantage of being able to control not only alternating current signals but also direct
current signals with lower leakage currents.
The basics of photorelays and precautions for their use are described in our application
note "How to replace mechanical relays with photorelays". Please also refer to this.
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Applications of photorelays to FA equipment
(Photorelay Application Point Image)
Application Notes
Fig. 1 Principle of photorelay operation
2. Output Terminals (I/O), Alarm output applications
In addition to the contact output units of programmable logic controllers (PLCs), general-purpose
inverters, servo amplifiers, various sensors, measuring and weighing equipment are increasingly
equipped with output terminals that control external devices and loads (Fig. 2(a), (b)).
Fig. 2(a) PLC Function Block Diagram
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Applications of photorelays to FA equipment
Application Notes
Fig. 2(b) Servo Amplifier Function Block Diagram
(Photo Relay Application Point Image)
2.1 Type s of output terminals
Typical output pin types are shown below.
1) Transistor/MOSFET outputs (sink type, source type)... Control of DC-load, responsiveness of
1 ms or so
2) CMOS high-speed output... Equipment control signal (serial communication, analog (PWM)
signal, etc.), response of 1 μs or so
3) Tr i ac output: Control of AC (alternating current) load, response of about 10 ms
4) Contact output (mechanical relay)... Control of DC/AC load, response of about 5 to 10 ms
5) Contact output (photo relay)... Control of DC/AC load, response of about 0.5 to 5 ms
This section describes the advantages of replace 1) transistor/ MOSFET output, 4) contact
output (mechanical relay) with 5) contact output (photorelay).
2.2 Application example of photorelay to transistor output terminal
Photorelays have mainly been used to solve mechanical relay problems, but in recent years,
photorelays have also been applied to eliminate the disadvantages of transistor and MOSFET
outputs.
The transistor and MOSFET outputs are used to output signals to weak electrical equipment
ranging from 12 to 48 VDC.
There are two ways to connect the power supply and load: a sink type in which current flows
from the load to the output terminal when the output transistor is turned on, and a source type
in which current flows from the output terminal to the load (Fig. 2.2.1(a), (b)).
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Applications of photorelays to FA equipment
and Common Board Sink Type
Fig. 2.2.1(b) Transistor output source type
Application Notes
In sink type, if the wiring connected to the equipment output terminal is grounded, load current
flows regardless of the status of the output terminal. In contrast, the source type is preferred in
European countries because it is highly safe because it is open to ground fault accidents.
In this way, the sink type and source type can be used according to the user's design philosophy.
However, since the wiring is different from each other, the assembly of the source type and sink
type must be changed according to the destination, and the contact must be changed manually
by attaching a switch on the board (Fig. 2.2.2(a) and (b)).
Fig. 2.2.1(a) Transistor output sink type
Fig. 2.2.2(a) Example of Transistor Output
Fig. 2.2.2(b) Transistor output/common board
source type example
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