Wireless Telemetry Systems can make measurements at inaccessible locations...
ones that may be distant, moving or dangerous, and deliver the result to you, as useful information, direct to your comfort zone, inexpensively.
If you want to measure something in a difficult place, the best way to do it is with a Telemetry System. If you don’t like the idea of running wires, or it’s impractical, then a wireless connection is the answer.
These systems are usually reliable, provided you follow a few simple guidelines. The main difficulty with wireless is... you can't see it, so the best way to avoid problems is to minimize the risks by doing things properly, from the beginning. Then you can reap the rewards.
The most basic system has a...
The measurement information is transmitted from the distant end and received at the local end. Electromagnetic energy, usually transmitted at radio frequencies (RF), carries the information.
At the measurement end...
there are usually two things:
A sensor or other device makes the measurements. For example, you may want to monitor the condition of a piece of machinery and use a sensor to measure vibration, to give an early warning of developing mechanical problems.
A wireless transmitter sends the measurement data to the receiving/processing end.
At the processing end...
A wireless receiver receives the measurement data transmitted from the measurement end, and...
A computer or other intelligent device stores the measurement data and processes it into useful information.
Radio Frequency energy (RF) usually carries the measurement information. You may use microwave telemetry or light, but these aren’t as common. Acoustic telemetry systems are sometimes used for tracking aquatic animals.
The types below show the options, benefits and issues associated with some of the available products.
At the measurement end...
Number of input channels.
Some products have only one channel, while others have several.
Different types of channel input.
You usually have the choice of analog, digital or serial digital... or a mix of these. Ensure the input to the channel is compatible with the output from the sensor or device that you want to use.
Single or separate packages.
Some wireless telemetry systems have the sensing and transmitting functions integrated into one module. Some types are more suited to this than others.
If you only need one sensor channel there are advantages in having everything in the one module. For example: a wireless accelerometer.
If you require several channels, then you’ll need several items - the transmit unit plus the sensors.
Streaming or Logging.
Some types of wireless telemetry systems can transmit a continuous stream of data from the measurement site. This is essential in some telemetering operations, such as monitoring race cars and other things that are happening fast, and need to be monitored in real time.
But because it’s continuous, you’ll need to supply more power than you would with the alternatives.
What are the alternatives?
Some wireless telemetry systems are able to store the measurement – a process called data logging. When you don’t need your information instantly, this can lower your power requirements. Important if supplying power is difficult at the remote end.
If you only require data occasionally, get a system that you can put into sleep mode where it’s off except when it measures and transmits. This will reduce your power supply requirements at the remote end.
If you store the data, the receiving end can request it, when required. Or the transmitting end may simply send it in small bursts.
The may be times when you want to have all of these options available.
At the processing end...
Single node or multi-node.
If you just want measurements from one location (one node), you only need a single node wireless telemetry system. But if you want to receive measurement information from several different locations, choose a wireless telemetry system that can handle that number of nodes.
Some software provides trouble-shooting information for you to use if you need help at setup, or problems occur during operation. Here are some examples...
Communication tests let you check that the radio connection is working properly.
Provision to make a manual sensor reading to verify that measurements can be received. This requires a wireless link that works in both directions (is bi-directional) since the request for a reading needs to be sent in the opposite direction, from the processing end to the measurement end.
Good wireless telemetry systems should also provide information about the health of the power supply at the measurement end. Important… You need to know the status of the power supply voltage so you can intervene before it’s too late. If it fails… no more information!
Some systems include data processing in their software. This may be quite specific, allowing you to easily process the measurement data and present it as relevant and easy-to-understand information.
Some useful things to consider are trending, averaging, maxima, minima and statistics such as standard deviation.
The Radio Link...
If you don’t want the bother of a radio license, wireless telemetry systems that work in the 2.4GHz (GigaHertz) band are a good choice, provided the transmitter and receiver are in radio range of each other. Though it may never be a problem, there’s something you need to be aware of... Interference.
You’d share this band with mobile phones, microwave ovens and other devices. However, digital spread spectrum technology and the ability to change channel, if necessary, will usually allow robust communications.
Other RF bands
These are also used for some wireless telemetry systems, though you may need a license, depending on the country you’re operating in.
The 5GHz band, opened up to relieve pressure on the 2.4GHz band, is becoming popular. It has fewer interference problems.
In general, the lower the frequency the longer the radio range. So in general, a 2.4GHz system will work over a longer distance than a 5GHz system.
At higher frequencies the RF energy is more easily absorbed or blocked by objects in and around the radio path.
Ideally a system should...
Here are some details...
Simple to set up and install
A good wireless telemetry system product should be easy to install. Ask the supplier about how to do this and assess whether you can do it yourself, or whether you need to include the cost of someone else installing it for you.
A good manufacturer will consider how a product is going to be used and installed, as part of the design, and supply excellent instructions that make installation straightforward.
There will be an antenna at each end and these may range from a small inbuilt antenna, for short range work, up to high-gain Yagis with many elements, similar to a TV antenna. Yagis focus the transmission and are used for tranmitting over longer paths. They need to be mounted externally on a building, or perhaps on a pole. If you don’t have enough signal, go higher. If you happen to own a satellite, a large parabolic dish may be more your style!
At the remote end, look closely at how the manufacturer recommends you connect the sensor (or other device), to the transmitting module, assuming they’re separate units.
How does the battery connect? Is it rechargable? If so, how does it get charged? For example, does it come with a solar charger?
At the base station, there may be special application software that you load onto a computer. The receiver is likely to connect directly to a USB socket on the computer via a standard USB cable. It doesn’t come simpler than this, but make sure the USB version (USB 1, 2 or 3) of the wireless telemetry system receive module is compatible with that of the computer, or the connection may not work properly.
Check that the specification of the computer meets the minimum requirements of the software, so that it will run correctly.
Robust – check the environmental rating
The wireless telemetry system remote end must be robust enough to survive in the environment you want it to operate in. If it’s cold, hot, wet, greasy or dusty, then consider what degree of Ingress Protection (IP) the Wireless Telemetry System will require.
If you’ll be using the sensor/transmitter outside, in the dust and rain, then ensure the IP rating should be at least IP66. Otherwise you’ll need to provide an enclosure to protect it.
Also, consider any exposure to oil or chemicals, and… If there’s any chance that the electronic package will have to survive in a pressurized environment, look closely at the IP rating. Consider an IP68 rating with the manufacturer’s recommendations for the specific product. .
Contact the manufacturer directly for advice if you’re unsure about this. They should know more about their own product than anyone else.
Consider the temperature range of the environment that you’ll be using the wireless telemetry system in.
Look at the extremes. If it has to work in sub-zero temperatures, then ensure that its specification guarantees it will work down there. If it has to work at elevated temperatures, make sure you choose a product that’s guaranteed to work at a higher temperature than the maximum you’ll be exposing the system to.
Compatible with sensors
The input must be compatible with the sensor output. So what types of sensor output are there?
Most fall into one of the three following categories...
Analog is still used but is the least attractive option. Sensors and other devices with serial digital outputs are superior and becoming common. Don’t use analog if there’s a digital alternative.
Analog is the way the physical environment works. Things in nature are usually continuous – analog - not sorted into bins according to their size! So why would we want to sort things into bins and call them digital?
Here’s why… If we sort it into bins, we can send it from one place to another almost perfectly - in digital form – as a number that represents the actual (analog) amount. The information is far less likely to be corrupted.
With digital, what you get is what was sent... mostly. Analog signals are susceptible to corruption by things such as electrical noise and voltage drop in cables.
The bottom lines... We try to convert analog signals to digital signals as close to where we’re sensing the physical analog environment as possible, as this minimizes the chance for the analog signal to be corrupted.
The quality of information transferred digitally is mostly superior to analog...
Analog is inferior, so if you can avoid it, do.
Stream, store, or download
Some wireless telemetry systems have multiple modes. They can stream real-time data continuously to the receiving end, or store it and download it later.
If you want to stream data, you need to choose a system that can carry the data at least as fast as the rate at which you want to make the measurements. Otherwise...
It’ll build up and you’ll get a buffer overflow!
Not need much power
Power is usually available at the base/computer end of your wireless telemetry system. Not always the case at the measurement end
If there’s no power already available at the measuring end, to run the electronics, you’ll need to provide it.
A wireless telemetry system should monitor its own supply voltage. The quality of the information depends on it.
Here are the most likely options...
Access to an existing power supply
If there’s existing equipment nearby, for example, electric pumps or other machinery, you may be able to get the power you require from here.
However, there are some disadvantages... You don’t have any guarantee of ongoing supply if it’s controlled by someone else.
You can reduce the risk by having your own battery, and just using the existing supply to trickle-charge it.
Also, it’s best to isolate your system from the other supply in case something goes wrong with it. You don’t want the other system to drag your wireless telemetry system down with it, or expose you to any electrical danger. There’s a better way...
Create your own supply. This puts you in control, and allows you to supply uninterrupted power... the preferred approach.
What are the options?
Non-rechargeable battery.With non-rechargable batteries such as alkaline, the main disadvantage is maintenance. Weigh up the costs and inconvenience of using batteries that need to be replaced.
Rechargable battery.You’ll still need a source of power. How much? You’ll need slightly more than the average power required by the electronics at the measurement end of the system.
No battery.Energy to power the system can be slowly built up by charging a supercapacitor, which is a bit like a battery that can be charged and discharged over a shorter timescale. Unlike a battery, it doesn’t wear out.
This is only suitable for sensor/transmitter combinations that require very little power. Because they transmit infrequently, on average, their transmit power is low.
Enough energy can sometimes be obtained from the environment. For example you can get solar energy from the sun or scavenge it from waste heat in a factory.
Not need a radio license
Want to be license free? All other things being equal, who wouldn’t?
If you can, choose a wireless telemetry system that uses a radio frequency of 2.4GHz (GigaHertz) and anyone, anywhere in the world, can operate it without a license.
Some, but not all, countries are license-free for other bands too.
Sufficient radio range
The range is the maximum distance you can position the transmitter from the receiver, where the wireless telemetry system still works.
It depends a lot on the application. A manufacturer can make recommendations, but has little control over where you place the transmitter and receiver, and what obstacles lie between them.
The product manufacturer may specify transmitter power and receiver sensitivity, in Watts and dB, but this means little to most people. It’s better to give the expected maximum line of sight distance between transmitter and receiver.
Line of sight...
is when the transmit antenna and the receive antenna can see each other – nothing’s in the way.
But what if you don’t have a clear line of sight?
If you could see them, radio signals would look a bit like light and shade. Objects between the transmitter and receiver may absorb some of the signal, or perhaps block it completely.
Like light, RF can bend around some objects, often allowing enough to get to the receiver, for the information to be fully recovered from it.
The RF energy only carries the information.
Our ability to recover the information perfectly only depends on enough of the RF signal reaching the receiver. Enough is all you need, and it may only need to be a very small proportion of what was transmitted in the first place.
Easy to upsize
It’s best to think about this at the beginning.
Even if you just want to measure one thing now, it may be that in future you need to expand your wireless telemetry system to measure more than one thing.
Here are the possibilities...
Perhaps you’ll want to measure more points at the same location, orWant to telemeter at a number of different locations, or both.
To measure more points at the same location...
your wireless telemetry system will need to have enough input channels of the right type.
The questions you need to ask about the system are these...
How many input channels does it have?What types of channel are they? Are they compatible with what I’m connecting?
To telemeter at several different locations the receiving end will need multimode capability so the system can handle the data sent from each of these remote nodes.
Have a great user interface
You don’t want to have to work too hard to understand your information.
The information displayed should be obvious… you want to understand what it’s telling you… at a glance. You don’t want columns of numbers that make you work to get the information you’re looking for, life’s too short!.
You want graphics... a picture that hits you between the eyes with the bottom line... or at the least a warning message...
Warning! The vibration level has exceeded your maximum. Replace your bearings. How many ways can you interpret that?!
And having a few analytical tools in the software suite is useful, but likely to be for specific applications. In the example above you may see some intimidating terms such as Fast Fourier Transform Analysis. Don’t be overawed by this. You don’t need to understand the maths behind it, just the message… and how it can be a good benchmark against which any future changes can be compared.
In many cases, all you need is the capability to produce a graph, showing you the big picture over the time period that interests you.
Easy to integrate with other systems
This is important if you want to send your information to another computer, whose specific role may be to carry out another function, perhaps an administration or hazard management operation, based on the information it gets from your wireless telemetry system.
Whatever you want to measure, here’s the important bit...
The files you send from wireless telemetry systems need to be compatible with the computers they’re being sent to, or they won’t make any sense to them.
Files are usually appended with a suffix known as the file extension and will be in the form filename.xxx, where xxx is the extension.
Quality of the product
Wireless telemetry systems that you’re considering should comply with an appropriate international quality standard for design and manufacture.
ISO9001 is a good example as it’s the most significant quality standard in the world. It’s used by about a million organizations in around 200 countries.
And a final comment
...on the range and accuracy of the sensors that you may want to connect to wireless telemetry sytems...
Check the manufacturer’s specification data sheet to ensure that your measurements won’t exceed the range specified for the product.
For example, if you want to measure temperatures of up to 220 degrees, don’t choose a temperature sensor with a range of 0 to 200 degrees. The likely consequence of this is that all temperatures above 200 will either flat-line and be recorded as 200 (even if they’re 205, 219 etc) or an intelligent system might report over-range or error.
Ensure that the overall accuracy you require can be achieved by the wireless telemetry system you’re considering before you buy it.