Remote Management:: telemetry monitoring using GSM devices PDF Print E-mail
Written by CMR Projects   
Friday, 16 April 2010 17:21

GSM TELEMETRY – UNDERSTANDING THE BASICS


Ever wondered what is happening to your remote, unmanned site? Ever wonder how you can turn the lights ON or your secuirty system or your irrigation pump? The answer is easy and, as yet, seemingly not explained too well by the manufacturers of such systems that can help. Let us try and pop the bubble and explain all to those of you who would like to be able to monitor and control your remote site.

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The type of system we are referring to here is a telemetry system and the definition of this, at least according to Wikipedia, is:

The automatic transmission and measurement of data from remote sources by wire or radio or other means (synonymous with telematics). It is a technology that allows remote measurement and reporting of information transmitting the measured value to a distant station, and there interpreting, indicating, or recording the quantities measured. The word is derived from Greek roots “tele” = remote, and “metron” = measure .


The principle of any GSM based telemetry system is to have a “cellphone” type device attached to the “real world”. In this way the telemetry system is based on the same technology that you use for your cellphone except that instead of using voice we use SMS messaging (or “text” if you are from the UK and insist on changing the original definition).


Real time data telemetry is often used when your remote site sends data to a monitoring source every 10 minutes or so using GPRS technology but this is quite a complicated solution and will not be covered here.


Simply put, we detect an alarm condition – say an over temperature or high humidty in your agricultural tunnel and get the system to send you an SMS to your cellphone such as:

 

HIGH Temperature at Leaf Plant-A, #14 Smith Street, Grabouw, Western Cape

 

Signing expensive and complicated cellphone contracts is NOT required, save to say that if you go to a respectful Vodacom outlet and ask for a Vodacom Messenger package. They will give you a SIM card on a 24-month contract for R35.00/month. This package has been specifically designed for GSM telemetry and offers SMS’s at R0.22/each. Peace of mind for R35.00!

 

Of course you could use a “pre-paid” SIM but what happens when the telemetry system detects a serious alarm condition and there is not enough money in the air-time to send the message!


OK so far – detect alarm condition and get the telemetry system to send an SMS to you. Now here comes the clever bit. GSM based telemetry systems can be used for any purpose:

  • Flow
  • Pressure
  • Temperature
  • Humidty
  • Security
  • Pump control
  • Air conditioners
  • etc. etc.

So you need to get an alarm that is meaningful so that you, or a colleague, can react accordingly.

 

It is thus pointless to get a message “Alarm on Input-1” rather get one as shown above that has relevance to what you are monitoring. Users should thus be able to change this simple text message “over the air” and without necessarily having to program the system using a PC or laptop.


Sending the unit an SMS, now there is a possibility…

 

#it1!LOW Flow!

 

Should change the text on a change in status on Input-1 to LOW Flow and the next time Input-1 changes state you know that the flow rate is too low. You only have to send this SMS once as the system will save the new message format in its own internal memory.


The clever thing about this is that the GSM system sends your own cellphone number attached to the SMS (text message) whether you like it or not and so the telemetry system can be programmed to ONLY accept SMS’s from a dedicated and authorised cellphone number. No hackers or un-authorised people allowed here!

 

That should give you an idea of how the inputs work and that they can be used for virtually anything, as the list above implies.

 

What about the OUTPUTS? Now these can be used, as per INPUTS but the other way around. Rather than the unit detecting an alarm and sending you an SMS, you can send the unit an SMS and get the system to react to it. Using outputs we can turn ON/OFF:

  • Pumps
  • Air-conditioners
  • Heaters
  • Humdifyiers
  • Lights
  • Fans
  • etc. etc.

An example here is probably the best form of an explanation of using input and outputs.


A client of ours runs a wine farm in the Western Cape. He has an irrigation dam that is used to feed a pump that irrigates the vines, when required. About 6Kms away, and down the hill near the river, he also has a pump station that he uses to pump water up the hill to the irrigation dam.


Previously he used a farm worker, suitably equipped with a bicycle, and solely employed to watch the dam level when they were irrigating. Thus when the dam level was going low the farm worker got on his bicycle and cycled the 6Kms down the hill to the pump station to switch the pump ON. He would then cycle back up the hill and watch for the dam to fill up, repeating the process cycling up and down the hill to turn the pump station ON or OFF for the entire duration of the irrigation program.


So this went on for many years until one day the farm worker got side-tracked, by his girl friend we are led to believe, and he forgot, during a particulary hot period, to turn the pump station ON, the dam ran out of water and so did the vines !!!


Today that particular farm worker is permanantly with his girl friend and the entire irrigation dam water level and pump station is controlled by a simple GSM based telemetry system. Now, after the installation of two separate GSM telemetry systems, when the Estate Manager receives a “LOW WATER” SMS from the first system on his dam he sends a “PUMP ON” SMS to his second system on his pump station, and the dam fills up. The manager knows that he has just turned the pump station ON as the telemetry system sends him an SMS confirming the status as such.


In fact it gets easier than that as OUTPUT-1 just has to be called “dial the telemetry number”. The telemetry system drops the call, thus costing you nothing, and checks to see if you are a valid user, if YES then it toggles OUTPUT-1, i.e. ON -> OFF or OFF -> ON and informs you accordingly via SMS.

 

It gets better than that, the story does not finish there. Our client went to the UK on holiday to visit his friends in London and forgot to change the number that the telemetry system reports to. There he was sitting in a pub in Earls Court London (where all South Africans in London seem to congregate) and he received an SMS from his irrigation dam to say that the water level was low! Much to his friends amusement he then sent the pump station an SMS to turn ON the pump.


Now you must be getting, or have got, the picture… easy monitoring of your plant, equipment, computer room, house etc. using standard cellphone (GSM) techniques.

 

Administrator: CMR Projects supplies the Cellcomm-104 unit with 10-inputs and 4-outputs with SIM socket, including a maintenace free rechargeable battery, charger and GSM antenna for R2,350.00 + VAT, excl. courier