Telemetry brings distance closer

With the growing acknowledgement of global warming and the effect it has on our climate, in particular our precious water resources, there is now more than ever a realisation of the importance of water conservation.

Telemetry has emerged as an integral tool in managing water resources efficiently for today's farming community. Telemetry cannot only be used to switch water pumps on and off, it can also be used to monitor water levels and sound an alarm when the water level becomes critical.

Another common use of telemetry is for remote-reading water flow gauges.

While the importance of telemetry for managing water resources cannot be underestimated, there are many other uses for telemetry that can make the life of the modern day farmer easier.

It can be used to control the operation of electric fences, monitor the status of gates at remote locations and remotely read instruments.

UHF radio (450-520 MHz) has proved to be the perfect medium for delivering telemetry services due to its propagation characteristics. In conjunction with the ability for UHF to be solar powered, it makes a remote installation totally independent of power and mobile phone technology.

The 12.5/25 kHz channel bandwidth and the near line of sight characteristics of UHF allow ranges of 30 km to be quite achievable depending on local topography.

When range is limited due to the local environment, a standard telemetry radio can be reconfigured to serve as a 'store and forward' repeater, thereby increasing the range to meet the system requirements.

We at GME use a standard 10 tone selective calling protocol (CCIR) with proprietary packet structure for data transmission.

This method is simple and robust, delivering greater range and good error-free transmission when using lower data rates than is normally achieved with conventional digital systems.

The transmitted signal contains the address ID of the station being called and the input/output ports being addressed, as well as the command or request message being sent or received.

The first five tones form the standard selcall of the end-point radio to be contacted and the next five form the telemetry command.

The outstation repeats the message back to the base station to confirm it has been correctly sent.

The base station can be pre-programmed to retransmit the message a given number of times until the outstation confirmation reply is received. If no reply or an invalid response is received, an appropriate warning message is sent to the user.

Each end-point radio is nothing more than a standard commercial PMR radio equipped with a relay/optoisolated input box. Each radio can have up to eight individually addressable inputs and outputs.

Using these affordable and seemingly simple elements can create a reliable point to point system. In addition, by using the in-built output reset timers and loopback options, advanced multipoint telemetry systems are also possible, without the need for dedicated PLCs (programmable logic controllers).

The farming community's requirement to be able to remotely manage plant and equipment is continually growing, and hence the uses for telemetry are endless and new applications are driven by imagination and the farmer's desire to save time and money.