Why is Temperature Profiling Important?
Charge and discharge currents increase the temperature of the batteries and temperature directly affects the lifespan and storage capacity of batteries. Batteries tend to be efficient and provide a normal life span at room temperatures. When batteries are subjected to cold temperatures, their capacity is greatly reduced and as temperatures increase above room temperature, their life span is reduced. At extreme temperatures, batteries can break down in several stages; leakage, smoke, fire and explosion. Manufacturers often perform abuse tests to determine the temperatures for each of the stages of breakdown.
Why Choose a DAQ for Temperature Measurements?
You can make basic temperature measurements with an Infrared Digital Thermometer, or a Digital Multimeter (DMM) with a thermocouple hooked up. So, why choose a DAQ instrument? It’s beneficial to use a DAQ when:
- You need to measure multiple temperature points in a single setup.
- Other types of measurements such as voltage, current, resistance or frequency, are necessary in the same test setup.
- You need to perform data logging over a period, and memory space is a potential issue.
When and How to Select a Multiplexer for Temperature Measurements
Multiplexers allow a single measurement system to measure multiple channels. Temperature measurements often use several thermocouples or other sensors, so multiplexers provide a great way to connect each one to the measurement system.
- Select a multiplexer with a built-in thermocouple reference junction when you need to obtain absolute temperature measurements. Keysight’s 34901A and 34902A offer this built-in capability.
- Scanning speed of up to 60 channels per second is sufficient for most temperature measurement applications. If needed, faster scanning is available with 34902A multiplexer, up to 250 channels per second.
- Multiplexers can also measure temperature using thermistors and RTDs. More accurate measurements can be made using 4-wire ohm measurements. The 349701A and 34902A are capable of both 2 and 4-wire ohm measurements.
Comparison of Keysight’s multiplexer cards: 34901A, 34902A and 34908A.
Choice of Temperature Sensors
The 34970A and 34972A DAQ models have universal inputs with built-in signal conditioning circuitry and software algorithm. This gives you the flexibility to choose from a range of temperature sensors.
Popular thermocouple sensors types are the type B, E, J, K, N, R, S and T. Depending on the test environment, some thermocouple types are more suited for use over others.
Resistance Temperature Detector (RTD)
You have a choice of 2-wire and 4-wire type RTD sensors. Use the 4-wire type RTD sensor if your leads are very long as this can affect the accuracy of temperature measurements. RTD sensors are known for having superior stability, accuracy and resistance-temperature linearity over other temperature sensors.
Thermistors are more sensitive than thermocouple or RTD sensors but are not as linear as an RTD. Common thermistors types include 2.2K Ohm, 5K Ohm and 10K Ohm.
Comparison between the three types of temperature sensors: thermocouple, RTD and thermistor.
Considerations for Temperature Data Logging and Analysis
As a DAQ instrument needs to be connected to a PC, some software applications are necessary for instrument connection, configuration and data logging. An application that provides visualization, graphing and reporting capability can also be beneficial.
Several test vendors offer software applications to connect, control and automate test instrumentation. Keysight offers BenchVue software, which provides an intuitive user interface so you can quickly set up and execute tests, and then get results faster. The Test Flow feature allows you to build your own automated tests, reducing significant test development time.
The BenchVue Data Acquisition Control & Analysis app can be used for data acquisition, data logging and data visualization. The app provides multiple data visualization displays and math capabilities, making it a powerful time-saving tool for instant monitoring, analysis and reporting.
The BenchVue Data Acquisition Control & Analysis app can replace much of the manual work required of an engineer from instrument configuration to report generation.
BenchVue Data Acquisition Control & Analysis app’s configuration setup panel
BenchVue Data Acquisition Control & Analysis app’s graphical display panel with strip chart
For More Information
Please visit our YouTube Channel, Keysight General Purpose Instruments for videos on temperature measurements and temperature profiling.