Wireless enabled sensors maybe the future of measurement technology communications as the internet of things becomes a bigger part of how electrical equipment is interconnected.
But any nascent engineering technology will have many limitations when compared to the existing long established alternatives it is aimed to replace.
Sensors are no exception to this rule, and this article explores the many advantages of wired sensors compared to wireless sensors in order to help you make a decision on whether to opt for a wireless sensor network over a wired sensor installation.
Obstruction effects
The connection to a wired sensor can be run through or around obstructions such as walls and equipment and there will no noticeable difference in performance. However wireless sensors are very sensitive to obstructions since high frequency electromagnetic waves cannot pass through solid objects without some signal loss. The thickness and density of a material is a major factor in contributing to a poor wireless signal. If obstructions are combined with a greater distance between the connected wireless devices, the signal will be totally loss at a much closer distance than suggested by the manufacturer’s specification.
Lower radio frequency interference from other wireless devices
Although wired sensors can be affected by radio frequency interference, but it takes a strong signal and close proximity to the RF source to impact the signal, especially if the wired connection is shielded by a grounded screen surrounding the wires inside the cable.
Wireless transmissions are sharing the same air space filled with RFI from other devices such as walkie talkies, mobile phones, broadband WiFi and microwave transmitters. Due to the tight controls on wireless transmission frequency bands, it is common for more than one device to be transmitting at the same frequency. This crowding of wireless signals can lead to significant interference with a wireless sensor and may lead to total loss of wireless communications.
Fast signal response and reading update rate
There is a wide range of update rates and frequency responses available for wired sensors. There is negligible effect on frequency response if a wired sensor is moved further away, whereas a wireless sensor will degrade response in order to maintain filter increasing noise levels. Since some wireless sensors have internal batteries, a higher reading update rate will consume more power and run down the battery faster.
Featured wireless measurement products
IWR-PORT Wireless Sensors to Ethernet, RS232 or RS485 Gateway Receiver - The IWR-PORT Ethernet Gateway provides a link between wireless sensors and sensor networks and Industrial Ethernet or RS-232/485 networks.
IWR-5 Five Channel Wireless Sensor to 4-20mA or 1-5Vdc Output Signal Receiver - The IWR-5 is a five channel receiver designed to pair with IW series of wireless sensors and provide a 4-20mA or 1-5Vdc output signal
No limitation on distance
Although there are limits to how far you can carry a wired signal without significant signal losses or interference, it is possible to run wiring much further than wireless connections due to transmission power constraints and how the signal strength degrades over distance due to the inverse-square law.
Smaller size
Wired sensors are smaller than wireless sensors because they do not have the additional components required to communicate the signal wirelessly and provide the power to supply the sensor and transceiver.
Lower power consumption
Wired sensors typically do not require a lot of power to operate and will operate on low dc voltages and use very little current. It is therefore possible to provide the power required remotely via the same relatively thin lightweight wiring that carries the sensor signal. Wireless sensors require an internal battery or a local power supply, and the current consumption will be greater in order to power the transceiver.
Lower cost installation
There is an extra cost associated with a wireless sensor installation. There are extra components inside a wireless sensor to convert the analog or digital signal to a wireless signal. If the wireless sensor is internally powered there are also the extra components required for the battery compartment and re-charging circuitry.
There is also the cost of the receiver which may often be required as an extra piece of instrumentation in order to convert the wireless signal back to another type of wired signal to make it possible to connect to other instrumentation.
Of course this extra cost can be offset by the cost of fitting cable for wired sensors. But it would have to be an installation with long tortuous cables runs, or one that requires the use of a specialised cable, for it to get close to the extra cost of installing wireless sensors and a receiver.
Featured wireless measurement products
IWPT Wireless Battery Powered Pressure Sensor and Receiver - Wireless battery powered pressure sensor and receiver system for connecting pressure sensors without wires to a central wireless receiver which converts each received pressure signal channel to a 1-5Vdc, 4-20mA output, USB, Ethernet TCP, RS232 RTU, RS485 RTU or 2G 3G 4G mobile cellular network.- IWR-5 Five Channel Wireless Sensor to 4-20mA or 1-5Vdc Output Signal Receiver - The IWR-5 is a five channel receiver designed to pair with IW series of wireless sensors and provide a 4-20mA or 1-5Vdc output signal
Compatibility between manufacturers
Once a technology is established, a consensus on the signal standards to adopt is formed by manufacturers, engineering standards organisations and customers. For wired sensors which have been around for a very long time, there are many types of compatible measurement instrumentation available on the market, and they all include support for the most popular wired sensor signal types.
Wireless sensors are in the early stages of industry adoption, and there are many types of proprietary wireless protocol which are specific to a particular manufacturer. This closed engineering development approach to wireless communication protocol ties the user into using only one brand for all the sensors used with a central wireless receiver.
No influence on other wireless devices
It is likely that wireless signals are already present in an area where you plan to use wireless sensors, due to walkie talkies, mobile phones, broadband WiFi and microwave transmitters. The addition of more wireless devices will introduce further potential for wireless interference and may lead to issues with existing working wireless connections. Wired sensors send low powered signals through cables and will not contribute any significant interference to wireless devices.
More choice for every application type
There are a plethora of wired sensor designs, approvals and engineering standards that have been nurtured over many years for nearly every type of sensor application. If you have an application for a sensor, there is a very good chance there is a wired sensor out there already that will meet, or can be easily adapted, to meet all your requirements.
In comparison wireless sensors are a very new and underdeveloped technology in terms of the possibilities of applications. It will be a long time before wireless sensors can be used in extreme or critical applications, and the majority of early product development will be directed at less demanding installations where the convenience of a wireless solution outweighs all the advantages of wired sensors.
Featured wireless measurement products
- HVAC chilled water wireless pressure monitoring in BMS - Upgrade your Building Management System with a reliable wireless pressure sensing system. This case study explores the implementation of a 0-10 bar gauge wireless transducer and receiver pair for HVAC applications, highlighting the 'plug and play' installation and long-term, low-maintenance operation.
IW Series Industrial Wireless Measurement System - A complete wireless sensor and receiver system for use in industrial applications.
