FAQ’s About STEUTE’s Industrial-Grade Wireless Components
In the past, the majority of wireless industrial control devices available have been for the monitoring, transmitting, receiving and processing of continuously variable (analog) parameters such as temperature, pressure, flow, humidity and speed. More recently an array of wireless components has emerged that generate and receive simple “on-off” signals for start/stop control, presence/position sensing, counting, alarm signaling, high/low level detection, and other desired digital inputs.
This is now changing with the development and introduction of a number of robust, reliable digital switches, sensors and related accessories.
With their availability, interested users have posed a number of questions as they strove to become familiar with the design, performance and application of these new control solutions.
The following represent a compilation of those most frequently asked questions as they relate to our family of industrial-grade wireless components and accessories (e.g. receivers, range extenders, antennas, power supplies, field strength monitors). We trust that they will be of value in understanding if and how these devices may satisfy your application requirements.
Should you not find the answer to your question(s), or need additional information, please do not hesitate to contact us. We will be pleased to address your requirements.
QUESTION 1: What types of functional wireless devices are currently available?
ANSWER: STEUTE’s present range of wireless industrial-grade control components include:
- Limit switches*
- Miniature position switches
- Non-contact magnetic sensors
- Non-contact inductive sensors
- Pull-wire switches*
- Push button command stations*
- Selector switch command stations*
- Key-operated switch command stations*
- Foot switches*
- Door handles with integrated push buttons
- Universal wireless transmitters
- Receivers with relay outputs
- Receivers with bus-compatible outputs
- Range extenders
*Energy harvesting (battery-less) units
QUESTION 2: What is “energy harvesting”?
ANSWER: Energy harvesting refers to the capturing of available sources of energy (such as wind, light, mechanical motion, thermal energy, et al) and storing/converting it into other forms of energy (such as electrical) for use as needed. Well-known energy harvesting devices include solar cells, wind turbines and hydroelectric generators.
QUESTION 3: How do the STEUTE wireless switches operate without a battery power source?
ANSWER: Those wireless switches designed for battery-less operation use “energy harvesting” techniques for powering the devices’ transmitter electronics. For STEUTE, these techniques are the use of a solar cell or an “electrodynamic energy generator” to respectively convert light energy and mechanical energy into electrical energy.
QUESTION 4: What is an “Electrodynamic Energy Generator” and how does it work?
ANSWER: STEUTE’s electrodynamic energy generators are typically a design element of those wireless switches characterized by mechanical actuation … such as limit switches, foot switches, or pull-wire switches. The “generator” consists of a permanent magnet and an electrical coil. The mechanical actuation of the switch moves the magnet through the coil, generating an electrical current in the coil. This electrical energy is sufficient to allow the Transmitter to send wireless “telegrams” (control signals) to the Receiver, process confirmation of receipt of the signal by the Receiver, and resend the signal if its receipt has not been confirmed.
QUESTION 5: What is the typical mechanical life an “electrodynamic generator”?
ANSWER: STEUTE’s proprietary electrodynamic generator designs have a mechanical life expectancy in excess of 1 million actuations.
QUESTION 6: What is the battery life for those devices that are battery powered?
ANSWER: Battery life is a function of several factors. These include battery cell size, battery energy density and the frequency of switch/sensor actuation. Depending upon the specific STEUTE switch or sensor, the battery life can range from several months to several years. Typical battery life for various duty cycles is provided with our device specifications.
QUESTION 8: Why don’t the wireless Transmitters have UL or CSA certification?
ANSWER: STEUTE’s wireless Transmitters (switches & sensors) are of such low energy/low power that they do not represent a safety hazard and do not require UL/CSA safety Certification.
QUESTION 9: Are STEUTE’s wireless industrial components suitable for use in machine guarding/safety applications?
ANSWER: Such applications typically require redundant signals to meet the safety Standards. Hence they would need to have independent, redundant control signals … each operating at its own unique frequency. Since most of STEUTE’s wireless devices operate at a single frequency (e.g. 868 MHz or 915 MHz) they are not intended, nor suitable, for use in safety applications. The sole exception at this time is our safety foot switch which frequency hops in the 2.4 GHz band … providing the redundancy required for safety applications. The current design is safety-rated at SIL Category 2, Performance Level PL d.
QUESTION 10: What is the typical transmission distance for these wireless devices?
ANSWER: Due to the diversity of installation environments and conditions, wireless device manufacturers cannot state an absolute transmission distance for a given transmitter. However, for evaluation and comparison, they typically provide nominal transmission distances indoors and outside (in “free air”). Depending upon the model of transmitter, STEUTE’s nominal indoor transmission distance is in the range of 30 to 50 meters and their nominal outdoor transmission distance is in the range of 400 to 700 meters. Actual transmission distances will be affected by structures and/or equipment in the wireless signal’s path. If in doubt of the efficacy of the application, it is suggested that the user conduct an in-situ evaluation of the Transmitter(s) and Receiver(s) in their specific situation. STEUTE offers hand-held, “signal strength monitors” to aid in this process.
QUESTION 11: Can these transmission distances be increased?
ANSWER: Yes. STEUTE offers “Repeaters” for this purpose. Up to two such Repeaters can be used to extend the transmission range between a Transmitter and the Receiver to which it has been paired.
QUESTION 12: What is the effect of various construction materials in the transmission path of the wireless telegram?ANSWER: Since the wireless signals are electromagnetic waves, some signal attenuation is not uncommon from the Transmitter to its Receiver. In addition to the signal strength being inversely proportional to the square of the distance between the Transmitter and its Receiver, sensing range can be affected by walls/objects in the transmission path.
Typical signal attenuation (at our operating frequencies of 868 MHz and 915 MHz) for various materials of construction are shown below.
|Materials||Typical Signal Attenuation|
|Wood, gypsum, uncoated glass||0 to 10%|
|Brick, stone, press board||5 to 35%|
|Armored concrete||10 to 90%|
|Metal, aluminum lamination||90 to 100%|
QUESTION 13: What is a “Repeater”, and what is its benefit?
ANSWER: A “Repeater” is a signal amplifier that can be located at some point in the Transmitter to Receiver signal path. It extends the range between the Transmitter and its Receiver.
QUESTION 14: Are tools or instruments available that can aid in the evaluation/installation/maintenance of a STEUTE wireless system?
ANSWER: STEUTE offers a Field Strength Monitor for this purpose. While it does not have the “gain” of the Receiver and its’ antenna, it will enable a user to identify the Transmitter, count telegrams received, see the relative strength of the signal at various points in the transmission path and to confirm receipt of the transmitted signal at the wireless Receiver’s location prior to actual installation of the Receiver.
QUESTION 15: What is a “Field Strength Monitor”?
ANSWER: STEUTE’s Field Strength Monitor is a portable, battery-powered, hand-held receiver that can be used to check wireless signal strength at various distances/locations from the Transmitter and aid in the installation of the wireless components. It features a digital LCD display (e.g. to identify the Transmitter being monitored, provide an indication of the signal strength in % at that location, and display the number of telegrams received from the specific Transmitter being monitored). It is a useful tool for evaluating, installing and maintaining STEUTE wireless systems.
QUESTION 16: At what frequencies do the STEUTE wireless industrial control components operate, and why were these frequencies selected?
ANSWER: STEUTE’s wireless Transmitters (switches & sensors) for non-safety applications are available for 868 MHz and 915 MHz operations. These are the preferred frequencies for industrial control in Europe and the USA-Canada respectively. STEUTE’s safety-rated foot controls utilize frequency-hopping technology in the 2.4 GHz band (accepted worldwide).
QUESTION 17: How does STEUTE’s SW868 MHz and SW915 MHz wireless technology differ from other single-frequency wireless protocols?
ANSWER: STEUTE’s SW868 MHz and SW915 MHz Transmitters and Receivers are designed to operate bidirectionally. Upon receipt of a wireless signal, their Receivers transmit a “signal received confirmation signal” back to the Transmitter. The Transmitters have the ability to process this confirmation of receipt,and to re-send the signal should the receipt of the transmitted signal not be confirmed. This bidirectional capability adds a heightened dimension to the system’s reliability. In addition, STEUTE’s electrodynamic energy generators are designed for industrial-grade switch life expectancies (more than 1 million actuations).
QUESTION 18: What output signal options are available from STEUTE‘s range of wireless Receivers?
ANSWER: STEUTE’s current family of Wireless Receivers include units with discrete relay outputs, PNP, TCP/IP, USB and RS232 Serial outputs. Other output protocols are in development and will soon be available.
QUESTION 19: How does one establish a communications link (e.g. “pair”) a STEUTE Transmitter with one of its’ wireless Receivers?
ANSWER: “Pairing“ is easily accomplished through a brief series of pairing steps using the front-panel accessible and easily-operable programming buttons and built-in status LEDs on the Receiver. For example, the steps to pair a Transmitter (switch/sensor) with STEUTE’s 915 MHz single-channel Receiver with discrete relay outputs include:
- Press programming button on the Receiver for 1 second. Green LED flashes slowly (2Hz).
- Actuate wireless switch/sensor being “paired” (taught in). Orange LED flashes.
- Press programming button again for 1 second to exit “pairing” (teach in) mode. Green LED stays lit.
QUESTION 20: How does one remove a Transmitter from a Receiver with which it has been previously “paired”?
ANSWER: Removing a previously “paired” Transmitter is easily accomplished through a brief series of steps using the front-panel accessible and easily-operable programming buttons and LEDs built into the Receiver.
- Press programming button on the Receiver for 5 seconds. Green LED flashes quickly (5HZ).
- Actuate the wireless switch/sensor to be deleted. Orange LED flashes.
- Press programming button again for 1 second to exit “delete” mode. Green LED stays lit.
QUESTION 21: How many Transmitters (switches/sensors) can be monitored by a single Receiver?
ANSWER: STEUTE’s discrete relay output Receivers are designed to accept signals from up to ten (10) individual Transmitters per channel. Thus a single channel Receiver can monitor up to (10) different switch inputs controlling its output relay. A four-channel Receiver can monitor up to (40) different switch/sensor inputs … (10) inputs for each of its four discrete output control relays. Bus-compatible Receivers offer the possibility of monitoring up to 40 individual SW868 MHz or SW915 MHz transmitters.
QUESTION 22: What is the response time from switch/sensor actuation until the Receiver output changes state?
ANSWER: Typical response time for STEUTE’s SW868 MHz and SW915 MHz devices is less than 10 ms. Typical response time for STEUTE’s 2.4 GHz multi-channel, frequency-hopping technology is less than 200 ms.
QUESTION 23: What is meant by “bidirectional” communication?
ANSWER: STEUTE has designed many of their Transmitters and Receivers to communicate in both directions … e.g. from the Transmitter to the Receiver and from the Receiver to the Transmitter. This capability enhances system reliability. For example, it enables the system to be designed such that Receivers can send an “acknowledgement signal” to the Transmitter upon receipt of its transmitted signal. Should the Transmitter not receive this acknowledgement signal within 16 ms of its original transmission, it can resend the telegram a second time.
QUESTION 24: What is the minimum number of components required to realize a wireless control function?
ANSWER: A system requires a Transmitter, a Receiver, a Receiver antenna, and 24 VDC power for the receiver. The Transmitter may be any of STEUTE’s many wireless switches, sensors and command devices. A Universal Wireless Transmitter is also available for integration of commerciallyavailable, cabled, dry contact devices as well as 24 Volt PNP devices.
QUESTION 25: What steps has STEUTE taken to optimize the reliability of their wireless industrial automation components and systems?
ANSWER: The following are among the available design features of STEUTE’s industrial automation component program intended to optimize reliability:
- Use of bidirectional communications between Transmitters and Receivers (e.g. acknowledgement signals, redundant transmissions, et al)
- Use of short telegrams to minimize in-air time
- Use of battery charge status monitoring
- Use of transmitter “status” signals
- Use of frequency-hopping(for 2.4 GHz devices)
- Use of unique, encrypted telegrams from each Transmitter
- Use of listen-before-talk (LBT) technology
QUESTION 26: What is the benefit of STEUTE’s listen-before-talk (LBT) technology?
ANSWER: STEUTE’s listen-before-talk technology has been designed for those applications involving a large number of Transmitters where the probability of simultaneous transmission from one or more Transmitters is high. This feature repeatedly listens to determine if there is another telegram at the same frequency in the air, prior to sending its telegram. If it detects the presence of another telegram, it waits a programmed interval, and listens again … sending its telegram when no other telegram is present. In so doing it greatly reduces the possibility of losing a telegram due to a “collision” … enhancing system reliability in highly (wireless component) populated applications.
QUESTION 27: What is STEUTE’s Universal Wireless Transmitter, and how can it be used?
ANSWER: Depending upon the model, STEUTE’s Universal Wireless Transmitter can also be used with sensors and switches that feature a normally-open dry contact or a PNP output. The transmitter converts the sensor/switch output signal to a wireless telegram compatible with our family of 868 MHz and 915 MHz Receivers. It is available as a battery-powered unit, or for use with 10 VDC to 30 VDC power input. The batterypowered unit can be used with STEUTE’s family of wireless inductive sensors or with conventional cabled switches having a normally-open dry contact closure. The external voltage powered unit can be used with conventional cabled switches having a normally-open dry contact closure or cabled 24 VDC sensor PNP output.
QUESTION 28: Is a programmable logic controller or computer required?
ANSWER: For many simple applications, it is not necessary to have additional control logic. STEUTE Receivers are equipped with up to 4 programmable form C relays … each with a maximum load rating of 6A/250 VAC, 2A/24 VDC.
QUESTION 29: How may STEUTE wireless equipment be used in a PLC or computer operated system?
ANSWER: There are several approaches to interconnect STEUTE wireless into a system. Receiver relay contact outputs may be used as direct inputs to the control system. STEUTE also has available Receivers with RS232 and TCP/IP communication protocols. Information regarding the data telegram structure is available for download from our website at www.steutewireless.com.
QUESTION 30: If a system requires each wireless Transmitter to be recognized independently, is it required to have a contact output available for each device?
ANSWER: It would be possible to do this using our multi-channel Receivers equipped with a relay output for each channel. However, for more complex applications, using the network communications capabilities of the selected Receivers may be more suitable.
QUESTION 31: What are some of the applications that have benefitted from the use of STEUTE’s wireless components?
ANSWER: Since these devices are relatively new, many potential applications have yet to be identified and realized. However, the following are among the applications already experiencing benefits of the wireless technology:
- Valve position monitoring
- Remote crane control
- Remote point presence or position sensing
- Assembly station inventory management systems
- Fire vent position monitoring
- Tank level monitoring
- Hatch and access port monitoring
- Hopper flap/diverter monitoring
- Safety shower/eyewash station alarm monitoring
- Rotary machinery
- Automatic door control
- Adjustable cut-to-length control
- Door monitoring
- Presence/position sensing in explosive environments