JohdotaJohdota device guide
Devices used in control circuits
What each device does, what its terminal numbers mean and how it is wired. Every device links to levels where you can wire it yourself. The guide follows IEC practice; choose your region to see what is different in your country.
01Control and signalling devices
SPush-buttonsStart and stop push-buttons, contact blocks and push-button colours according to IEC 60204-1.→SEmergency stop buttonHow an emergency stop button works: a latching mushroom-head button, direct opening contacts and a reset before restarting.→SRotary and selector switchesMaintained rotary switches, spring-return switches and the Hand-Off-Auto selector switch, and how to read a switching table.→HIndicator lightsHow to wire an indicator light from terminals X1 and X2, and what indicator light colours mean according to IEC 60204-1.→
02Relays and contactors
KAuxiliary relayHow an auxiliary relay works: coil A1–A2, changeover contacts and the plug-in socket.→KContactorA contactor is an electrically operated switch for motors and other large loads.→KTTimer relayOn-delay and off-delay timer relays: supply A1–A2, control input B1 and the delayed contact 15–16–18.→KImpulse relayAn impulse relay changes state on every control pulse.→KCounter relayA counter relay counts pulses and switches its output when the preset is reached.→
03Motor supply and protection
QSwitch-fuseA switch-fuse is a switch with built-in fuses.→QMotor protection circuit breakerA motor protection circuit breaker (MPCB) protects a motor against overload and short circuits.→FThermal overload relayA thermal overload relay protects a motor against overload.→QLocal isolatorA local isolator next to the motor: isolation for maintenance work, locking in position 0 and the early-break auxiliary contact.→MInduction motorThe three-phase squirrel-cage induction motor: rating plate markings, star and delta connection in the terminal box, and changing the direction of rotation.→
04Monitoring and sensors
APhase failure and monitoring relaysA phase failure relay checks that all three phases are present and in the right sequence.→ASafety relayA safety relay monitors an emergency stop on two channels.→SLimit switchA limit switch stops a movement at its end position.→BSensorsSensors in control circuits: level, pressure switch, photoelectric sensor, twilight switch, thermostat and door contact, and how to wire a three-wire sensor.→
05Automation
PLCSmall PLCSmall PLC supply L+ and M, 24 V DC inputs, relay and transistor outputs, the program scan, ladder diagram and the addresses I, Q, M, T, C, AI and AQ.→BTransmitter 4–20 mATwo-wire connection of level, pressure and temperature transmitters, scaling, live zero and NAMUR NE 43 fault limits at the analogue input.→UVariable speed driveA variable speed drive sets the speed of an induction motor and starts it on a ramp.→YSolenoid valvePneumatic 5/2 and 3/2 solenoid valves: monostable and bistable, 24 V DC coil, ISO 1219 symbol and port numbers 1–5.→APneumatic cylinderDouble-acting pneumatic cylinder, its control with a 5/2 solenoid valve, the magnetic piston and position sensors that tell the PLC the end position.→