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Wireless / Radio comms with digital panel meters, large displays and message displays - a guide

Wireless digital panel meters and large displays

This discussion covers wireless transmission of data over modem links operating in 433, 868, 902-928, 2400 and 5000 Mhz, but could apply to other frequencies.

This article is not intended to be negative or to discourage wireless communication. Instead, we hope it will help you to consider some of the challenges which wireless systems can present, which may not be immediately apparent to you, so that you can plan for success.

It would be beneficial in many installations to use a wireless communication link between devices, to save on cabling costs or to allow greater freedom of movement.

Examples can include communicating between a load cell amplifier and a large display on a moving crane, or from a pallet counter to a display in a fork lift truck.

We have a number of handy solutions which suit the many different site conditions you might encounter.

This guide is intended to make you aware of some of the important things to consider when planning wireless systems, because a wireless link might be unsuitable for your application, and it is better to realise that before you design and install your system.

"Wireless systems cannot afford to be trivial, unless the application is trivial."

Wireless radio signals - their nature.

Wireless modem devices usually operate in the UHF or Microwave radio bands and are limited by law in the amount of power they can radiate.

UHF and Microwave energy is similar to light in many respects...
  • It travels in a straight line.
  • It doesn't pass through metal or foil insulated walls, or steel reinforced concrete.
  • It reflects off metallic objects which can cause destructive interference.
  • There are often many interference sources in an industrial environment
  • It reduces in strength by 4, each time you double the distance between transmitter and receiver.
  • It can be difficult to gauge the absolute quality and reliability of the link
  • If something moves between the transmitter and the receiver, the signal can be blocked
  • If another transmitter comes close to the receiver, it can 'blind' the receiver
  • If more wireless networks are later installed in the area, reliability can drop due to interference.
  • Simple wireless modems are vulnerable to interference and are not private.
  • If something reflective moves nearby (not between) the transmitter or receiver, the signal can drop due to destructive interference caused by your own signal!

Wireless links - are they for you?

Mobile phones and WiFi operate at similar frequencies to wireless modems and you will know from experience that signals can be frustratingly unreliable in certain places. The same is true for wireless modem signals - they are vulnerable and simply not as reliable as wired links, especially in a complex industrial environment.

This is a simple fact of physics, so you can't ignore it and hope for the best. But if you know about it you can plan to achieve the best possible reliability, to avoid nasty surprises. Or you might decide that a wireless link is unsuitable for your application.

Wireless communication is a compromise, where we take the convenience of having no wires as being worth the risk of not having perfect reliability. It is not a 'simple' system like a cable, it involves quite complex technology which can be harder to fault-find and correct than a broken cable.

Streaming limitations
Many wireless links are restricted by law in how often they can transmit. However, experience shows us that in many cases, the law is ignored and some devices greedily take up channel bandwidth, depriving other devices from legitimate occasional transactions.

If you need to stream data, WiFi is generally a good medium, as it is more tolerant of other devices operating nearby, but its range can be quite poor.

Getting the best reliability out of wireless links

Now that we realise the limitations of wireless links, and we have chosen a suitable application which does not require total reliability, we can look at ways of getting the best reliability we can, in the environment it will be operating in.

The most important things for improving reliability are...

  • Site the transmitter and receiver as close to each other as possible
  • Eliminate fixed and moving obstacles between the transmitter and receiver as much as possible
  • Use external directional antennas if possible, visible to each other, pointing at each other.
  • Mount antennas away from other electronic devices
  • Use frequencies which are not in use nearby, to minimise interference
  • If you can route several nearby addressable devices through a single modem, that is preferrable to having individual wireless modems for each device
  • Do not mount wireless antennas in metal enclosures
  • If privacy and security is important, https over WiFi is the de-facto method.
  • If one-way communication of an analogue variable signal is acceptable, T24 is suitable.
  • For better interference tolerance, use modems with error correction and agile frequency hopping, such as WiFi or T24.
  • For 2-way comms, if you need confirmation that your message has arrived, WiFi is suitable.

Might you need to add other devices to your wireless network?

If you want to expand your network and include other devices, they will all need to use the same communication protocol and transport layer. What will it cost to include the same wireless system in those devices, if they don't support it as standard? Is that actually possible?

Will you need a custom data-translator or gateway?

Can you extend your wireless network distance if you need to?

Systems change. If you need to extend the distance between devices on your wireless network, or need to talk around a corner or through a wall which wasn't there before, is that easy to do? Can you add additional routers in the signal path to extend it?

Do you need a license for your wireless network?

If you have a challenging application, where high power is required in order to achieve reliable communication, you may need a license.

Are you relying on batteries to power your wireless device?

If you lose your wireless link because the batteries have failed, will there always be someone on hand who will be able to diagnose that reason and change batteries fast? Will they be able to source the batteries quickly? Will your wireless device be easily accessible when the batteries need changing? Will the device need re-configuring if its batteries have failed? Does everyone know how to do that?

What happens if you can't get replacements in the future?

When one of your wireless devices fails in the future, will you be able to get a drop-in replacement?

Will it use a protocol developed and supported by one manufacturer? Will that device still be in production? Will the manufacturer still have stock? Or will it be a generic protocol supported by many manufacturers, so alternative sourcing is possible?

Is data security important to you?

If your data is important and you want to avoid it either being intercepted or maliciously corrupted (hacked) you should transport it over a secure transport layer.

Being wireless, the data is spread over a wide area, for anyone in range to intercept. Similarly, your receiver could be in the capture zone of signals sent from devices you have not authorised, or may not be aware of.

The de-facto means of achieving secure wireless links is via the https protocol on WiFi. We use this method in our cloud based applications between the clients and the server.

You cannot hope to achieve similar security between 'simple' devices, as appreciable computing power is needed to achieve the encryption and decryption.

If security is important, please contact us with your wireless requirements and we will be happy to help with a system which will give you the best possible reliability and security to suit your application's needs.

We may advise against a wireless link, if it would be unlikely to give the reliability or security you need...
In which case, we will offer alternative solutions.

REMEMBER - wireless communication is a compromise, involving many judgements between the need for security, reliability, distance, cost of installation and cost of maintenance.

There is no single ideal solution - every case is different and needs its own careful, considered judgement in choosing the solution with the best fit to your wishes.

If you are happy to accept that wireless systems are a compromise, they may be for you! They are probably NOT suitable for you if your application is safety related or if you could lose unacceptable amounts of money if the link is lost or unreliable, for any reason.

Coming Soon...
Arranging the parts of your wireless system from beginning to end for best performance.

We will look at where the best places are for siting the components of a typical system...

The beginning of the link...
  • Power Supply
  • Sensor
  • Cabling from sensor to signal conditioning
  • Signal conditioning
  • Display
  • Data output port
  • Wireless transceiver
  • Antenna

The end of the link...
  • Antenna
  • Wireless tranceiver
  • Data input port
  • Destination device
  • Output signal conditioning
  • Cabling from signal conditioning
  • Display
  • Power cabling
  • Power Supply

The answers are not as simple as you might think and need careful thought and planning for each application. More soon...

We look forward to hearing from you!

Graham Laming signature
Graham Laming
Application Engineer

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