What does a hand off auto switch do?
Hand-off automatic switches are used to select the function of a motor controller either manually or automatically. In the OFF position, the motor does not run at all. In the AUTO position, the motor runs whenever the two-wire control device is closed. An operator does not need to be present.
How does the control circuit remain on after the start push button is released?
The three-wire control circuit is the most widely used motor control circuit. This control circuit gets its name because of the auxiliary contacts that are connected in parallel with the start button. The auxiliary contacts seal in the circuit to keep the coil energized after the start push button is released.
What are HOA switches?
The function of a HOA (Hand-Off-Auto) selector switch is to control whether a motor is in hand (manual) mode, auto mode, or off. To operate the motor while hand mode is selected, start and stop push buttons are usually used.
What is an automatic control circuit?
Also known as two-wire circuits , automatic control circuits can be controlled manually from simple two-wire ON/OFF toggle switches or any number of two-wire pilot devices such as temperature switches or float switches. Some examples include sump pump circuits and temperature circuits.
What does Hoa mean on a switch?
Hand-Off-Auto
One of the most basic, yet often misunderstood, components of a control system is the simple HOA (Hand-Off-Auto) switch. Undoubtedly there are many installations in which multiple control switches are needed in different areas of the plant in order to control a single field device.
What’s an HOA switch?
What is the difference between a power circuit and a control circuit?
Power circuits are identical for most 3-phase motor starters, so it is common not to refer to them in schematic drawings . In contrast to the control circuit, the power circuit provides the large values of voltage and current used by the motor itself. A device that controls the flow of electrical power to a motor.
What is Hoa in Control Panel?
One of the most basic, yet often misunderstood, components of a control system is the simple HOA (Hand-Off-Auto) switch. Undoubtedly there are many installations in which multiple control switches are needed in different areas of the plant in order to control a single field device.
What is Hoa in automation?
The inherent problem with the term HOA, according to Niemi, is that it combines Location of Control (the designation for hand/manual operation) with Mode of Control (the designation for automated operation) on the same switch.
Where is the hand off auto switch located?
The second switch, out at the control station itself, could then be labeled as “Hand-Off-Auto” which would designate the Mode of Control. In “Hand” the motor would run continuously and in “Auto” the motor would start and stop by a PLC or other controller. A modulating valve has a control switch labeled “Hand-Off-Auto” located near the valve.
How are the relays in a control panel activated?
These relays are activated by pulse commands from a controller or momentary switch closure. The relay contacts are mechanically latched in the closed position and the load will remain on in the event of a control panel failure period.
When to use optoisolated series of relays?
The optoisolated series of relays may be used when the controller does not have sufficient coil drive power available to energize a relay of the desired contact rating.
What happens to a relay when power is lost?
The relay contacts are mechanically latched in the closed position and the load will remain on in the event of a control panel failure period. If power is completely lost the contacts will remain in their last state and the load will activate upon the return of normal power or emergency power.
