Hazardous Location Switches
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To introduce Honeywell hazardous location switch products
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Hazardous Location Switches
- 6. Proximity Sensors vs. Industrial Limit Switches Proximity Sensors Industrial Limit Switches No Touch Sensing Limit switch requires actuation from target. However, wide variety of actuators that will not obstruct the target. No contact bounce Most interface circuits have buffers to ignore contact bounce. Easy to interface to PLCs No pull-up or pull-down resistor required for limit switch interface. High speed sensing Limit switch max actuation up to 100 – 200 ops per minute which covers more than 80% of applications.
- 8. Features & Benefits Feature Benefit Rugged and industry sealed housing Prevents contaminants from entering, and protects switch through repeated wash downs Precise actuation Needed to control machine movement and operation Long mechanical life Eliminates costly downtown for failure and replacements Explosion proof Works well in hazardous vapor locations
Notas do Editor
- Welcome to the training module on Hazardous Location Switches .
- This training module will introduce Honeywell BX2 hazardous location switch products.
- Simple circuit requirements can be solved through either single pole, single throw or single pole, double throw possibilities. In some control applications, circuit requirements need only one circuit to be controlled. As a result, all that’s necessary is a switch designed to control a single circuit conductor, a single pole switch. If it merely needs to open or break a circuit or close or make a circuit, then all that’s needed is a switch with one moving contact and one stationary contact, a single pole, single-throw switch (SPST). There are two options when choosing the single pole, single throw (SPST) switch. The single throw could be normally in contact with the movable pole, when the plunger is in the free position. This type is a normally closed (NC) switch. Or the single throw could not be normally in contact with the movable pole when the plunger is in the free position. This type is a normally open (NO) switch. Besides single pole, single throw choices for simple circuit problems, there’s also an option which allows a single pole, single circuit switch to control not one but two circuits. This is accomplished by introducing a second stationary contact or throw switch into the switch housing. Instead of a single pole, single throw switch, there’s now a single pole, double throw (SPDT) switch with both a normally closed and a normally open contact. This contact arrangement gives the added bonus of circuit flexibility. A single pole, double throw (SPDT) switch can be wired to imitate either or both of the two contact arrangements in a single pole, single throw switch.
- Some applications move beyond the simple options just mentioned to equipment that might require switches with not one but two independent control circuits. If this is the case, the solution could be double pole, double throw switches which simultaneously make and break two independent circuits. With double pole, double throw (DPDT) switches, circuit flexibility with several wiring possibilities and a significant savings in space and weight is accomplished because each pole is provided with a normally open and a normally closed contact. Beyond the DPDT choice with more circuit problems, Honeywell offers additional circuit alternatives for more specialized applications. If circuits must be switched without any interruption in the current flow as, for example, in an extremely slow moving timer where a momentary interruption might result in the dropping out of a relay or a malfunction in some machine apparatus, then a make-before-break contact arrangement becomes a logical alternative. Circuit continuity in this single pole, double throw (SPDT) switch is maintained through a momentary overlap of circuits. When switching from one throw to the other, the normally open (NO) circuit is closed before the normally closed (NC) is open. The double-break switch, unlike most switches which interrupt a circuit at only one point, makes and breaks a circuit at two points. To accomplish this, the load is carried through the contacts at both ends of a butterfly spring. As the plunger is depressed and released, the contacts make and break the two circuits involved. Double break switches are often found in industrial types of applications since they are thought to give added insurance to the breaking of circuits.
- Honeywell offers an advanced line of heavy-duty limit switches and a wide selection of application-proven enclosed switches. The rugged switches are suitable for use in harsh-duty, wash-down environments, while the sealed versions keep out moisture and other contaminants. These products meet or exceed critical standards, which allows them to be used globally. Enclosed switches are known for their high precision and low cost. Limit switches are especially rugged and well sealed, allowing explosion-proof switches to be used in hazardous locations.
- This chart illustrates the primary features of proximity sensors compared to Honeywell limit switches.
- Honeywell explosion-proof switches are designed specifically for use in hazardous locations. They are easy to apply, customize, and troubleshoot. To comply with explosion-proof requirements, the flame path within the housing is designed to contain and cool the escaping hot gases that otherwise could cause an explosion outside the switch. The explosion-proof switch design also ensures the electrical arc, or spark created at contact is never exposed to the outside atmosphere. Switches are available with the UL/CSA ratings for North America. In Europe the usage is governed under is commonly referred to as the ATEX directive. Emerging IECx global standard will replace all local explosion-proof standards. Honeywell products are well positioned to support this IECx standard.
- Key features of Industrial and Hazardous Location Switches for the industrial market include the rugged and industry sealed housing. This housing prevents contaminants from entering and protects the switch through repeated wash downs. The precise actuation of the switches meets the need to control the machine movement and operation. The switch’s long mechanical life eliminates costly downtime that would be caused if the switch failed and needed to be replaced. And finally, because the switch is explosion proof, it works well in hazardous vapor locations.
- The MICRO SWITCH™ BX2 Series features a 316L stainless steel enclosure that provides enhanced corrosion resistance in applications exposed to aggressive, caustic agents. The stainless steel housing helps protect the switch mechanism from corrosion often present in chemical processing plants, off-shore/near-shore sites, and other hazardous areas. The BX2 Series complies with the European Directive on Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres (94/9/EC) commonly referred to as the ATEX Directive. Compliance with the Essential Health and Safety Requirements has been assured by compliance with EN50014 1997 and EN50018 1994. MICRO SWITCH™ BX2 Series meets the North American Hazardous Locations Designation: Division I, Class I, Groups B, C and D; Division I, Class II, Groups E, F and G and comply with UL Standard: UL 894, CSA Standard: C22.2 No. 25-1966, C22.2 No. 30-M1986. The MICRO SWITCH™ BX2 is ideal for outdoor use or in adverse environments where a combination of explosion proof plus sealing requirements are needed. To comply with explosion proof requirements the BX2 has flame paths within the housing, which cool exploding gases below the ignition temperature before they reach explosive gases surrounding the housing. Flame paths on the BX2 are an extended plunger between the switch cavity and head and the cover-housing threads on the front of the switch.
- The MICRO SWITCH™ BX2 Series is ideal for outdoor use or in adverse environments where a combination of explosion proof plus sealing requirements are needed. The applications include process control where they can be used as control valves, petrochemical plants, paint facilities or waste handling. Agricultural industries include grain handling and grain conveyor applications.
- Thank you for taking the time to view this presentation on “ Hazardous Location Switches ” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more technical information you may either visit the Honeywell site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. You may visit Element 14 e-community to post your questions.