Temperature is usually an easy thing to understand and measure. It is a critical physical property that may have high impact on efficiency and environment. There are many reasons to both keep track of and control temperature.
Some applications where temperature monitoring may be of interest are listed here:
- Refrigeration systems – Automate temperature monitoring to eliminate manual checks. Get real-time alerts by email, text message or phone. Maintain compliance with log history, incident reports, and NIST calibration.
- Human environments – office, industrial or public spaces.
- Agricultural applications – freeze alarms, optimal growing conditions or animal environmental monitoring.
- Food safety – monitor and record temperatures for compliance and tracking.
- Museums, old/vacant buildings or vacation homes – monitor for freezing or out-of-bounds conditions and keep historic data for records.
There are several types of temperature sensors, suitable for different purposes.
There are several different types of thermocouples. Some are suitable for very low temperatures, down to -180°C, and some can be used to measure very high temperatures, up to +1500°C.
The principle for a thermocouple is that when a metal is subjected to a temperature differential, a voltage will develop. A thermocouple uses two wires of different metals, so that two different voltages are generated, and we can then measure the differential, which will be proportional to the temperature difference between the two ends of wire.
The generated voltage is very small – in the order of microVolts per degree – and to know the absolute temperature we also need a reference. The signal from a thermocouple needs to be amplified for the ezeio to be able to measure it. There are several manufacturers of thermocouple interfaces that can supply a suitable output signal for the ezeio system.
A thermistor is a resistor that varies its resistance with the temperature. There are two main types; those that increase resistance when the temperature rises (PTC), and those that decrease resistance the temperature rises (NTC).
Thermistors are typically suitable for moderate temperatures, like outdoor/indoor applications.
Thermistors are usually defined by their resistance at 25°C and a B-parameter. These two parameters can be used to convert the resistance to an actual temperature. However the relationship between temperature and resistance is not linear and the math required (the Steinhart-Hart equation) to do the conversion is not completely trivial.
The ezeio can be programmed to convert thermistor resistance to temperature. Scripting is required. eze System provides this as a standard support service. Supported 3rd party expansion modules for the ezeio have the conversion math built-in.
Resistance Temperature Detectors are usually very accurate and can be used to measure a wide range of temperatures.
RTD’s basically consist of a thin wire wrapped around a non conducting core, like glass or ceramic. The resistance in the wire will change with temperature. Different metals have different properties, but the nice thing is that the resistance-temperature relationship is very linear in a wide range, which makes conversion easier.
A common metal in RTD’s is Platinum due to it’s very wide linear range from almost absolute zero to 1000°C. Platinum based RTD’s are also referred to as PT-sensors.
The resistance of an RTD only changes a fraction of an ohm per degree, so a sensitive amplifier is required to boost the signal to something that can be measured with the ezeio.
There is really no such thing as a purely digital temperature sensor. There are however integrated sensors that provide a digital output. These sensors can be calibrated at the factory and since the output is digital there is no error or loss in the signal.
The ezeio works with a type of digital temperature sensor from Dallas Semiconductor. These sensors are programmed with a unique serial number which allows our system to detect the type of sensor and automatically set up suitable configurations. These sensors are suitable for measuring from -55°C to +125°C and are available in a rugged waterproof steel casing.