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Far be it for me to discuss here what you, the tunnel user, should do to comply with the exact science of “climate control” but it is a subject that fits nicely into some form of GSM based telemetry monitoring.

Having hopefully grasped the issue of the basics behind telemetry techniques using GSM technology the question that remains in most peoples minds is “how do I monitor temperature and humidity ?”, however this aspect of electronic integration to a telemetry system is relatively easy.

There are many suppliers of temperature and humidity sensors, although as normal one has to watch out for those suppliers who think that they know what you want and insist on selling you a “solution” that probably won’t work, or has serious inaccuracies.

Complete solutions such as integrated humidity and/or temperature sensors can be quite expensive so please watch out for the chancers. The alternative to paying for these complete solutions is to purchase the individual elements such as temperature and/or humidity sensors, but then you will have to find a “friendly” electronic guy to design the solution to give your telemetry system an alarm contact for an “over or under temperature alarm” or “humidity alarm”.

These basic electronic temperature and humidity elements are quite common from reputable suppliers and one can find these on the internet. Over the years I have dealt with many electronic suppliers but the best I have found is Mantech Electronics. They have branches in JHB, CPT and DBN and you can find them at www.mantech.co.za. I would thus highly recommend them as an electronic component supplier, they stock a combined temperature and humidity sensor that costs around R45.00 (click here) that one can use to form the basis of climate control unit.

Temperature sensors are supplied in a plethora of formats – mainly analog devices output a signal in mV (milli-volts) proportional to the actual temperature (such as 10mV/Deg C) such as the LM35 from National Semiconductor click here or an actual digital signal such as the Dallas DS18B20 click here. The choice will be made by your electronic design company, but most will favour the analog device as being the most common, and possibly the cheapest.

Humidity sensors that I have dealt with over the years are all supplied in analog output only and typically range from 0-5Vdc for 0-100%, but there are many derivatives based along these lines. Honeywell offer a large range but, although these are great to use and are very predictable and reliable, typically these are quite expensive. It really depends on the accuracy that you need.

Having found the right supplier for a combined climate monitoring system, or you have got your electronic guy to design a system for you, you can now integrate quite easily to the GSM telemetry. The output from your climate monitor needs to have a normally open contact such that, upon an alarm condition, the contact opens and thus triggers the telemetry system to send an SMS.

In general if an overhead spray sprinkler system is used as a humidifier then your sending an SMS to the GSM telemetry system should turn this system on. The water flow for this humidifier can be simply controlled by a low voltage solenoid valve and these can be purchased from most respectable irrigation suppliers, such as Controlled Irrigation. These solenoid valves are normally rated at 24Vac and so one has to “switch” the supply to these solenoid valves using an external relay on the GSM telemetry system and a simple 230Vac/24Vac transformer (5amp rating or larger depending on the number of solenoid valves you want to turn on at the same time).

From my experience PLEASE put a 28Vac MOV (metal oxide varistor) across the solenoid valve as this will protect your system from surges and spikes as one finds are introduced to the system. Thinking that you are nowhere near any electrical storms is simply not enough. Municipality’s often introduce major spikes and surges when they switch their distribution circuits. A combination of solenoid valves and water is an ideal mix to attract the demons of spikes and surges !!!

Whilst you are at the spike and surge suppression story please also consider installing a surge protection unit on your electrical distribution board for your tunnel as this will save you big money in the long run. These are available from most electrical wholesalers but please do not buy from the corner shop. Stick to a reputable manufacturer like Surge Technology’s DehnGuard 275. For a single phase system you will need two such devices (one for the 230Vac live and the other for the neutral) for a 3-phase supply system you will need 4 such devices. They are priced at about R450.00 each, excluding installation, but should be considered as a “blue chip” investment. I have used these devices all over the country for some 15-years now and, once fitted, they hardly ever need looking at.

We had a client recently who was spending about R10,000.00/month on repairing/purchasing pumps/controllers etc. that had been damaged due to the effects of lightning (spikes, surges and the like), and this had been going on for 12-months!!!! Purchasing and installing 4 x DehnGuard 275’s for their 3-phase distribution board solved all of their problems and, for the last 6-months they have no problems at all.

Temperature control is a different animal and, as there are numerous ways to achieve the end result but it is difficult here to be specific, without my writing a thesis on the principals of climate control that UCT might give me a honorary degree for. Nevertheless a heating element is probably the basic element to be used here. Here we are talking some serious power and thus we must consider the switching currents. Remember that a 3KW element will be a 12 amp load and so your switching relays need to be suitably rated, 20 amps in this case. Please don’t rely on a device rated at 15 amps as any variation in the load specifications will get seriously close to the limit of the switching device.

Doubling up on the contacts of a 10 amp relay (possibly two or three parallel contacts) is possible, but frowned upon by the purists, as if one contact burns out for one reason or another then the full load current has to be handled by the remaining contacts. Please always “over rate” your switching devices – relays for water solenoid valves and/or heating elements, else you will have to add a fire alarm sensor to your GSM telemetry unit J

Cabling to/from the switching devices to the load should be kept to the manufacturers rating at all times. Don’t scrimp and save here as it will come back to bite you in the futureJ. Typically 1.5mm cable is rated at 15 amps, don’t try and use 1mm cable as you find that (a) the cable will get hot if overloaded and (b) a volt drop in the cable will create operational problems at the load end. For longer runs please consider using 2.5mm cable the cost is higher but worth it in the long term. Use an electrical wholesaler to buy 100M lengths, don’t bother with shorter lengths as you will pay more in the end.

A tip here, from my days of industrial installation, is that if you have to run one cable from point-A to point-B to a sensor or whatever then please run a “spare” at the same time. This will add costs to your initial installation but you will thank me later when, 6-months down the road when your tunnel is operating so successfully that you have to add another cable ! It will also act as a “spare” should the rodents come past for a light nibble….

Preventing the rodents having supper should be easy if you run all cables in at least 20mm light duty ABS plastic conduit and SEAL the joints against ant invasion and water ingress. Most 20mm conduit and fittings are available from electrical wholesalers and hardware stores. Jointing pieces such as “T”, 90ºbends and junction boxes are also available and use the type with “inspection covers” as this will be useful in the future for running additional cables or fault finding. Please don’t just run 3M lengths after 3M lengths with these as you will have a major problem pulling new cables and fault finding in the future. Inspection covers make life a lot easier.

If there is enough demand I can produce a temperature and/or humidity module that will be compliant with most GSM telemetry systems.

Article supplied by CMR Projects.