There is a whole lot of jargon around datalogging and monitoring systems that make sure you have no idea what your friendly "expert" is talking about. Hopefully the explanations below will help you learn the lingo and cut through the organic fertiliser product.
Datalogging is exactly what it sound like: the logging of data. It is the electronic form of your old weather diary where you manually recorded daily rainfall and soil temperature records. Datalogging technology has piggybacked on the wider computer industry so that a wide range of dataloggers are available for virtually any application and any price.
For those who want more detail, a datalogging system can be broken down into the following components:
Sensors - to measure the parameter you want eg an anemometer to measure wind, a temperature sensor, or a current transformer for power use
Processing electronics - to read the sensor and apply any calculations or calibration factors, a bit like a smart, programmable volt meter
Data storage - this can be retrieved as a file to be read on your computer. Data files generally consists of a simple "text" file containing lines of records where each line starts with a date and time stamp, and then the readings for that time. Depending on the datalogger, you may need specialist software to read the file, or you may be able to read it in a common spreadsheet program like Excel or OpenOffice.
Communications - there needs to be some way of retrieving the data from the datalogger. This can be by a cable between the datalogger and laptop, a display, or you could have some sort or remote telemetry (see below).
Application -actually the most important part of the system, is how the data is going to be used. This should define the rest of the system and could be research, consent monitoring, irrigation scheduling, frost alarming or any other.
For simple applications, a single unit will do all of what you require in one package, for more complex applications, a specialist will design a multi-component system. This is a bit the same as the difference between a small portable music player (Ipod or transistor radio depending on your age!) and a multi-component Hi-fi entertainment system.
Now that I have made it sound incredibly complicated, I can reassure you that all you need to decide is the application, what you want the system to do. Then you should be able to discuss with your provider what sensors and communication options will suit you best.
Telemetry refers to any means that you can get access to data without physically going to the station. These days there are many forms of telemetry including cell phone, land line, VHF/UHF radio, spread spectrum radio, wireless, satellite, ethernet, IP, GSM, GPRS, XT etc. Many of these terms are alternative names for the same thing so it helps to know your way around some of the terms. The choice of telemetry depend on the technology available, the up front cost, ongoing costs and availability of networks as provided by telcos such as Telecom or Vodafone.
Scott Technical can offer almost any of these options but the three most common in New Zealand these days are:
Cell phone telemetry (GSM) - the user dials up an 021 number at their station using specialist softare via a modem attached to their computer. Data is downloaded to the users computer. The hardware cost for this option is relatively small but the user is charged for every phone call. This charge is usually small however due to the small amount of data.
Cell phone telemetry (IP: GPRS or XT) - the user uses specialist software to dial up an "IP address" at the station to download data. The IP address is a little like a web address. Because there is so much traffic on the internet and there are security considerations (among others), normally the data is collected by a secure data collection service and provided to end users on a web site, or for ftp download. This option has similar hardware costs to GSM. There is also a fixed subscription fee for the data collection and web access.
Radio (spread spectrum) - to be exact radio communications covers a wide range of technologies including cell phones, any "wireless" device and tradiational UHF radios. When we are talking about spread spectrum radios, we are referring to radios that transmit for relatively short distances (a few km), with low power and no ongoing license fees for the user. Data is collected to the users local computer. Hardware costs for this option are higher than cell phone, however there are no ongoing costs.