Introduction to Pilot Devices

Pilot devices are mainly used in the commercial or industrial applications where human-to-machine interface is required. These comprise various types of selector switches, pushbuttons, pilot lights, signal beacons, as well as toggle switches. Based on their designs, pilot devices can be distinguished into two types: indication devices and actuation devices. And some devices provide both indication and actuation (ex: illuminated pushbuttons).

Typically used as a part of a system, automated process, or a control panel, these devices provide information on condition and control monitoring of different types of processes, machinery, and equipment.

Types of Pilot Devices

1. Pushbuttons – These are the control devices used to manually close and open a set of contacts. Pushbuttons are available with a variety of operator designs such as flush, extended, or mushroom head, with or without illumination. These devices are usually provided with normally closed, normally open, or combination contact blocks.
2. Pilot Lights – As the name suggests, these devices provide the visual indication about the operating status of a circuit. They are mainly used for ON/OFF indication, changing conditions, and alarm signaling. Pilot lights include a colored lens such as red, green, blue, yellow/amber, clear, or white. These colored lenses symbolize the condition of the machine or equipment to which the lights are connected. Pilot lights are also available in a variety of designs such as:
   1. Indicator: Equipped with incandescent lamps or LED’s, these lights are mainly used as indicating lights in automated instruments, condition panels, telephones, and dashboards.
   2. Relampable: These pilot lights feature a lens that can be replaced from the front panel of the lighted device in the indicator, once they stop functioning.
   3. Non-Relampable: As the name suggests, these lights are offered as one-piece device with fixed lens. It means the whole indicator needs to be replaced, if the lighted device stops functioning.
3. Selector Switches – These rotary devices are used to close or open contacts manually. Typically available in designs such as spring return, maintained, or key operated types, selector switches differ from pushbuttons only in their operation. The selector switches feature levers or knobs that are rotated to open or close the contacts, whereas pushbuttons operate linearly and have buttons for performing the same task. The contact blocks on the selector switches are typically interchangeable with those on the pushbuttons. These switches can be easily used to select one or multiple possibilities such as hand-off-automatic, high or low speed, run or stop, and up or down. Selector switches are available in two-, three-, or four-position types.
4. Emergency Stops – Designed to improve the safety of equipment and workers, these pilot devices are required by installation codes and standards, and are used to disable a machine or a system in the event of an emergency. Often referred to as emergency stop pushbuttons, these devices are mainly of two types: push-pull, and push-twist release.
5. Potentiometers – These devices feature three-terminal resistors with rotating or sliding contacts, which adjust the voltage sent to the machine.

Ranges of Pilot Devices

In the US, pilot devices are mainly categorized as modular or compact/monolithic based on their construction.

• Modular: These devices are designed such that each individual component can be selected and configured for a special purpose. Modular pilot devices enable pre-wiring, and are customizable, and flexible. They can be easily used in industrial environments, and are often designed to comply with UL Type ratings 1, 3, 3R, 4, 4X, 12, and 13. The most common sizes are 30 mm and 22 mm.
• Compact/Monolithic: These devices help OEMs save space and streamline their operational costs. Featuring all-in-one designs, these compact devices have limited functionalities. Unlike modular designs, compact pilot devices do not allow the flexibility of multiple configurations, and have unique part numbers.

Terminology of Pilot and Actuation Devices

Pilot Device Colors, Meanings and Functions

Indicator Light Colors:

Indicator lights and displays serve to give the following types of information:

• Indication – to attract the operator’s attention or to indicate that a certain task should be performed. The colors RED, YELLOW, GREEN, and BLUE are normally used in this mode.
• Confirmation – to confirm a command, or a condition, or to confirm the termination of a change or transition period. The colors BLUE and WHITE are normally used in the mode and GREEN may be used in some cases.
• Unless otherwise agreed to between the supplier and user, indicator (pilot) light lenses shall be color-coded with respect to the condition (status) of the machine in accordance with the following table.

NEMA, UL and CSA Enclosure Ratings

IEC Enclosure Ingress Protection (IP) Ratings

The IEC, standard 60529 defines Ingress Protection with a two di git code. The first digit describes the degree of protection against access to hazardous parts and ingress of solid objects. The second digit designates the Ingress Protection against water. Please refer to the appropriate sections of IEC 60529 for complete information regarding applications, features, and design tests.

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