When it comes down to determining temperature in environmental media, there are many options—from fiber-optic to infrared sensing technologies—to observe and quantify the relative kinetic energy of a material.
For single point data acquisition and a given specific temperature range and target medium, of course certain technologies are more optimal than others. When it comes to profiling temperatures in air, water, ice and soils what are the best options for collecting temperatures over time?
Thermocouples
Generally, for multi-point temperature acquisition, the minimum standard is the use of thermocouples. Thermocouples are temperature sensors that produce a voltage when a temperature differential is experienced by two dissimilar conductors at a specific location. The primary benefits of thermocouples are that they are precise, widely available and can integrate with a variety of data collection and storage devices. But, they also possess several limitations:
- Sensor count is limited by available multiplexer ports
- The connectors are more cumbersome as each sensor needs discrete pin-out
- Each thermocouple location requires a dedicated circuit increasing the amount of conductor wire needed
- A voltage is produced that needs to be post-processed as a temperature. Further manual note-taking, Analog to Digital (A-D) converters, multiplexers, network interface devices, and specialized knowledge are also often required
Thermistors
Thermistors (thermal resistors) provide another option for creating multi-point temperature cables. A thermistor is a resistor whose measureable resistance varies significantly with temperature. A voltage is passed through the device and the drop in voltage is correlated with temperature.
Thermistors are commonly used in a variety of environmental applications and share many of the same advantages and disadvantages of thermocouples. In addition, thermistors:
- Require a low current excitation source to register a voltage drop
- Are susceptible to self-heating
The Bandgap
An alternative to thermocouples and thermistors utilizes silicon bandgap temperature sensors that can be manufactured within an Integrated Circuit (IC). BeadedStream LLC manufacturers Temperature Acquisition Cables (TACs©) that utilize this technology.
- Relative to thermistors and thermocouples, the analog to digital conversion occurs on-board the sensor. No further A-D conversion is required and resistive losses (voltage drops) do not affect the temperature reading.
- TAC sensors relay temperature measurement data to a central microprocessor, using a lightweight digital communication protocol on a single wire lead.
- Each TAC sensor is uniquely identifiable, enabling many sensors to share a single wire. Regardless of the number of sensors used, TACs always only need three conductors.
- TACs are customizable and built to customer specification. Waterproof and rugged, TACs utilize the latest in arctic-grade materials to withstand the harshest environments.
TACs provide more sensor locations over greater lengths, while simplifying installation, reducing component counts and ultimately lowering project costs. In addition, TAC communication output can be converted to a variety of serial logic levels for integration with just about anything capable of industry standard serial communication protocols.
If you mind the bandgap, you log more data without logging the miles.
