It is evident that wireless technologies have been widely recognized and mastered in industry. New and advanced standards, the accessibility of a wide variety of devices, and the performance demonstrated by a broad installed base each prove their adequacy.
Nonetheless, while there are a variety of devices that can monitor, transmit, receive, and process continuously variable parameters (e.g., flow, temperature, pressure, etc.), there are very few ways that wireless devices can be used to generate and receive simple data. On-Off" signals for machine start/stop control, presence/position sensing, counting, alarm signals, process control and other required digital inputs.
This is now changing with the improvement and demonstration of a wide range of powerful and reliable digital contact and non-contact switches, sensors and related accessories.
Accessible and under development control components include:
- Mechanical limit switches
- Contact presence sensing switches
- Non-contact magnetic sensors
- Non-contact inductive sensors
- Photoelectric sensors
- Pull-wire switches
- Pushbutton switches
- Momentary and hold selector switches
- Key switches
- Foot switches
- Door handle systems with integrated push-button controls
The recognition of these new wireless digital control inputs is the result of a variety of significant professional improvements. Among them are:
- The design and production of robust energy harvesting mechanisms (energy generators) capable of meeting the duty cycle and life expectancy requirements typically encountered in industrial applications. Let us assume that a permanent magnet moves through an electrical coil as a result of the motion of a switching actuator. This generates enough electrical energy to transmit encrypted wireless telegrams to "paired" receivers within signal range. These generators are designed for an expected mechanical life in excess of one million operations, eliminating the need for battery power for a variety of mechanically actuated switches (e.g., limit switches, pull-wire switches, pushbutton switches, selector switches, key-operated switches, and foot switches).
- Design of transmitter electronics that require little power and allow two-way communication between the transmitter and receiver. Transmission protocols are characterized by short telegrams to achieve the shortest transmission durations.
- Use of solar or high energy density, long-life batteries (mechanical energy generators are not an option).
- Application and use of noise-resistant radio frequencies (e.g., 868 MHz, 915 MHz, and 2.4 GHz) that are nationally or globally accepted standards in industrial control applications.
- The design of field strength monitors that contribute to the efficient installation and maintenance of communication links.
Potential Benefits
Potential benefits offered by these control solutions include:
Lower installation costs - where eliminating materials (cables, connectors, conduits, cable trays, junction boxes, strain relief, etc.) and their associated installation labor can result in significant cost savings. This economy may be even more important for switches and sensors that are relatively far from the endpoints or that require armored, shielded, or other high-priced cables.
Reduced Maintenance Costs - Eliminating cabling also reduces the likelihood of cable damage and associated repair or maintenance costs.
Increased System Uptime - With reduced maintenance requirements, system uptime and productivity can increase.
Flexible Control System "Topology" - The availability of wireless switches and sensors allows control system designers to place digital inputs in locations that are remote and difficult to access via cable. In addition, switches can be easily added to existing machines or work cells.
New Potential Solutions for Selected EX Applications The inherently low power operating characteristics of the ...... allow the use of ATEX-IECEx certified wireless switches/sensors in selected explosion hazardous areas without the need for intrinsically safe barriers, encapsulation, or other costly protection methods.
New potential solutions for applications where cabling or cabling maintenance is considered impractical or economically unfeasible ...... For example:
- Remote areas where distributed power is not readily available.
- Rotating equipment where flexible cables are frayed or damaged.
- Rotating equipment that requires slip rings.
- Locations with extremely long cable runs or where installation costs are prohibitive.
Reduce Personnel Costs ...... Using wireless switches can reduce personnel costs in applications where digital information is now collected locally by humans. Examples include local field production counts and assembly station inventory status.
Typical and Potential Applications
Because these devices are relatively new, many potential applications have yet to be identified and realized. Applications that have already experienced one or more of these benefits include:
- Valve Position Monitoring
- Remote crane control
- Remote point presence or position sensing
- Assembly Station Inventory Management System
- Fire vent position monitoring
- Tank level monitoring
- Incubation and access port monitoring
- Hopper baffle/diverter monitoring
- Safety shower/eye wash station alarm monitoring
- Rotary machinery
- Automatic Door Control
- Access control monitoring
- Explosive environments
Application: Automotive Assembly Line Inventory Management System
In this application, assembly line workers at this location need several different components to complete each assembly. In the past, when additional parts were needed, they would place an "Inventory Request" card at the pickup location. Periodically, "messengers" would retrieve these cards and bring them to the storeroom, where the replenishment would be dispatched to the assembly cell.
The "messenger" is eliminated by placing wireless limit switches below the second "garbage can" location on each track, which contains multiple garbage cans for an assembly component. When the lead bin on each track is empty, it is physically removed to allow the next bin in the track to slide into the first bin position.
When the last part bin in each track slides into the first position, the second position in the track becomes vacant. The absence of garbage cans in the infeed track changes the state of the wireless limit switch, sending an encrypted signal to the central stockroom location. This signal alerts the stockroom that an additional quantity of the specific part associated with the received signal is needed.
The required parts are then sent to the assembly cell.
Realized benefits include:
- Low installation costs.
- Savings in personnel costs ...... Elimination of "messengers".
- Faster inventory replenishment.
- Reduced assembly cell downtime.
- Increased productivity.
Application: Valve position monitoring
Here, the open and closed positions of manually operated valves are expected to be detected and the corresponding control signals sent to the control center of the natural gas pumping station.
control center of the gas pumping station.
For this purpose, two wireless electromechanical limit switches are fixed to the valve head.
Each is actuated by a "flag/cam" mounted on the valve head.
By design, these ATEX-IECEx rated position switches operate at very low voltage and current levels.
By design, these ATEX-IECEx rated position switches operate at very low voltage and current levels ...... well below any power levels capable of producing sparks.
Each one sends a "safe" signal to a wireless receiver mounted outside the explosion hazard area.
Realized benefits include:
- Significantly reduced maintenance - no batteries or cables to replace.
- Lower installation costs - no need to lay and protect cables from the switch to the control cabinet.
- Lower component costs - due to the elimination of expensive Ex-rated cables and connectors.
- "Radio" signaling - allows the control cabinet to be located outside the explosion hazardous area.
- Safe operation in Zone 1 and Zone 2 explosion hazardous areas.
Application: Tanker Truck "Fuel Line" Position Monitoring
Similar wireless switches have proven valuable in tanker truck filling facilities at refineries. The goal here
is to ensure that the neck of the fuel filler tube is correctly positioned in the opening of the tanker truck being loaded.
above the opening of the tanker being loaded ...... prior to the start of the filling operation.
Initially, the fill tube position was monitored using the usual cable limit switches. While this solution was effective, the cable from the switch to the control panel would quickly wear out or be damaged by constant movement and/or fuel line wear. Replacing the "wired" switch with a wireless functional equivalent eliminated this problem, resulting in a reliable, robust long-term solution.
Accrued benefits include:
- Significantly reduced maintenance; no batteries or cables to replace.
- Low installation costs; no wiring or protective cables are required from the switch to the control cabinet.
- Safe and reliable operation in explosion hazardous areas