Lab 12: Low voltage control
Lab 12: Low voltage control
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Lab 12: Low voltage control.pdf
Part 1
Part 1
A relay is switch and a wire coil closing/opening circuits electronically for a low-power signal to control a higher-power circuit.
If we energize the wire coil (put current in it), it becomes an electric magnet, with a a metal piece attracts to the coil.
Instead of attracting a piece of metal, it attracts a metal switch, so the coil is energized by the push button, it causes a magnetic field to attract the right switch and close.
Note: Coils are simplified as a circle, instead of a wire coil:
The advantage to use a relay is the lef tcontrol circuit can be low voltage, a control circuit of 10, 5 V, or even be controlled by a computer.
The right one can be 120, 240 V. Any voltage we want is found by the source.
The type of switches used.
Part 2
Part 2
Diodes are electronic components letting current flow in only 1 direction.
Left diagram: For a diode to conduct, its polarity must be positive on the anode and negative cathode, which has currrent flow.
Right diagram: positive on cathode and negative on anode.
Conventional current flow only flows in its arrow symbol's direction.
If a circuit has AC sine wave, current only flows in positive half cycle (curve's yellow part) and not negative half cycle.
The left one can have current go through from left to right.
Right one cannot have current flow through as the second diode is backwards.
Test a diode with an analog ohm meter put the red lead on the anod the black lead on the cathod the cathode is the one with the stripe and on R * 1 it should give you it should conduct and it should give you somewhere under 20 Ω, here it's ~13 Ω. If we reverse the leads put the red lead on the cathode and the black lead on the anode that means it should not conduct and as this Omer shows on the right hand side it shows infinite ohms.
We can't test a diode with a digital ometer. We must set the digital meter to the dial setting to test a diode. The red lead on the anal and the black lead on the cathode (with the stripe) voltage it reads ~0.5-0.7 V, meaning it's properly conducting
If we reverse put the red lead on cathode and black lead on anode, the digital meter should read overload--it isn't conducting, so the dial works properly. We must use the diode chcker section of the digital meter as it raises voltage on oupuut
Checker section of the digital multimeter because it raises the voltage up on the output so the dial conducts.
The relay has parts moving like a motor. If we put current in 1 direction, its middle part truns counterclockwise. If we put current in the opposite direction, its middle part moves clockwise here.
Relay switch circuit diagram
Relay switch circuit diagram
In a 2-wire douglas relay lighing circuit:
This has a 2 wire switch, with an up and down button (one button but with 2 positions to it).
This diagram has two dials in the switch in opposite directions.
The circuit is fed by 24 V AC transformer, so the transformer's output polarities change each cycle at a point as a sine wave.
If the middle movement moves counterclockwise, it connects the 3 contact terminals on the left side.
Those are the contact to power the lighting circuit at the same time.
As it moves counterclockwise, its small tail piece moves from a diode to its opposite one.
It has also a latching pin to hold the inner movement in place so it becomes a latching relay.
What happens if we push the switch's top part in? The transformer's polarities varies. This case, if it changes the bottom as positive and top as negative, see that the current flow into the bottom diode in the relay into the switch's top diode and back to the transformer.
It also goes into the o
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