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PROBLEM SOLVING
Mirage technical manual
page 57 of 65
Solid state relay
The solid state relay (SSR, see Figure P 4) in the Mirage is a normally open electric relay without the
moving parts found in an electro-mechanical relay. When a (small) control voltage is applied to the
SSR, a LED illuminates which in turn switches on a photo sensitive diode. The diode current turns on
a back-to-back thyristor to switch the load. The optical coupling allows the control circuit to be
electrically isolated from the load.
Note!
The LED visible on the front of the SSR is an indicator light which is lit when a control current is
applied to the SSR. It is not the LED that triggers the diode.
A single-phase normal power Mirage Duette has 1 SSR which switches on 2 of the 3 heating spirals in
the heating element.
Triple-phase and high power single-phase Mirages have 3 individual SSR
’s: one for each of the three
heating spirals in the heating element.
See also
“electric scheme Mirage heating 1 phase” and “electric scheme Mirage heating 3 phase”.
In most cases when a SSR malfunctions, the load connectors are continuously coupled even when
there is no control voltage applied. This means that the heating element remains switched on even
when the temperature controller does not transmit a control voltage.
However, it has been known to happen that the SSR fails with the load connectors not coupling or only
occasionally coupling when the control voltage is applied.
Figure P 4. A solid state relay (left) as used in the Mirage and the heat transfer sticker (right) that
should be applied on the back of the SSR before mounting.
Upper connections (1, 2) are the load (connecting mains switch to safety overheating switch); Lower
connections (3, 4) are for control voltage (from the Stork ST25 temperature controller).