|| What are Solid-state Relays?
Difference between SSRs and Mechanical
SSRs (Solid State Relays) have no movable contacts. SSRs are not
very different in 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 and output signals. Photocouplers
change electric signals into optical signals and relay the signals
through space,thus fully isolating the input and output sections while
relaying 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.
・ They provide high-speed, high-frequency switching operations.
・ They have no contact failures.
・ They generate little noise.
・ They have no operation noise.
SSRs (Representative Example of Switching
for AC Loads)
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 not only mounted to
control panels, but also 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,Cycle
Control, Optimum Cycle Control,Phase Control)
ON/OFF control is a form of control where a heater is turned ON or
OFF by turning an 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 control where the heater
is turned ON and OFF at intervals of a few seconds over a period of
several years, then an SSR must be used.
With cycle control (G32A-EA), output voltage is turned ON/OFF at a
fixed interval of 0.2 s. Control is performed in response to current
output from a Temperature Controller in the range 4 to 20 mA.
The basic principle used for optimum cycle control is zero cross
control, which determines the ON/OFF status each half cycle. A
waveform that accurately matches the average output time is output.The
accuracy of the zero cross function is the same as for conventionally
zero cross control. With conventional zero cross control, however, the
output remains ON continuously for a specific period of time, whereas
with optimum cycle control, the ON/OFF status is determined each cycle
to improve output accuracy.
Enables low-cost, noiseless operation without maintenance
Enables noiseless operation with high-speed response.
Optimum Cycle Control (High-accuracy Zero
Many heaters can be control using communications.Enables noiseless
operation with high-speed response.
Phase Control (Single Phase)
Enables precise temperature control and increases the heater's
Precaution for Cycle Control and Optimum
With cycle control, inrush current flows five times every second
(because the control cycle is 0.2 s). With a transformer load, the
following problems may occur due to the large inrush current
(approximately 10 times the rated current), and controlling the power
at the transformer primary side may not be possible.
1. The SSR may be destroyed if there is not sufficient leeway in
the SSR rating.
2. The breaker on the load circuit may be tripped.
With phase control, output is changed every half-cycle in response
output signals in the range 4 to 20 mA from a Temperature
Controller. Using this form of control, high-precision temperature
control is possible, and is used widely with semiconductor equipment.
Configuration and Operating Principle of
MOS FET Relays
MOS FET Relays are SSRs that use power MOS FETs in output elements. In order to
operate the power MOS FETs, photodiode arrays are used as
light-receiving elements. When current flows into the input terminal,
the LED lights. This light generates a photoelectromotive force in the
photodiode array, and this acts as a gate voltage that turns ON the
power MOS FET. By connecting 2 power MOS FETs using a source common,
control of AC loads is possible. There are models for control of DC
loads, which have just one power MOS FET.
There is no varistor in the G3VM MOS FET relay for signalling.
This type of product has a relatively short history, and companies
use a variety of names and brands. The following table shows examples
for signals (equivalent to the G3VM).
||Name in catalog
|Matsushita Electric Works
||Photo MOS Relay
|OKI Electric Industry
||Photo MOS Switch
||Photo DMOS-FET Relay
||MOS FET Relay
Related Products: ABB
Electronic Relays / ABB
Relays / Siemens
Relays / Mitsubishi
Relays / Mitsubishi Overload Relays
Relays / Idec
SmartRelay / Idec Relays