- Batteries used in a wide variety of applications must be rigorously tested to ensure that they work properly.
- In this article, Ametek VTI Instruments explains why the characteristics of its EX1401 acquisition system are adapted to battery tests.
- Combined with the EXLab Express software, the EX1401 system acquires voltages and temperatures.
- It has an isolation level of 500V, and offers a sampling rate of up to 20 kS/s.
- Its 16 channels for voltage and temperature measurement are configurable by software.
Insulation against common mode voltages
To increase the operating life of the batteries, several cells are connected in series during the charge and discharge cycles. During the test, an acquisition system measures the voltage of each battery. This process can create a high common mode voltage, which, combined with common mode noise, can make the acquired data unreliable. Since the common-mode voltage is high compared to the actual battery voltage, it is difficult to distinguish noise from the actual battery voltage.
The EX1401 acquisition system for voltage and temperature measurement by thermocouple features 500V of insulation between channel and ground to ensure appropriate protection against high common mode noise. Each channel is isolated and has input protection under a variety of operating conditions. This contributes to the accuracy of the measurements and protects the instrument against harmful voltages.
Sampling and measurement
The battery test requires the measurement of the slew rate. To measure this parameter, the batteries tested are charged and discharged several times while an acquisition system measures the battery voltage. These acquisitions make it possible to plot the discharge curve of the battery and calculate the expected life of the battery and the number of charge/discharge cycles.
To obtain a precise battery discharge curve, the test must measure the battery voltages at a sampling frequency of at least 1 kHz over a long period of time. At the same time, it is necessary to monitor the battery temperature to ensure that it does not heat up and cause damage when it discharges quickly. Since temperature measurement systems do not generally support high voltage levels and do not use high sampling rates, voltage and temperature measurements are usually performed with separate instruments.
The EX1401 can sample signals up to a speed of 20 kS/s, allowing voltage variations to be captured every millisecond, and thus the battery slew rate to be calculated. Each channel is independent and configurable by software. Each of the 16 channels can be configured independently to measure voltage and temperature over different ranges. The same instrument can be used to measure temperature and voltage. It can be used to connect and test several batteries simultaneously. Each channel of the EX1401 is equipped with its own 24-bit resolution analog-to-digital converter. All channels are synchronized.
Software configuration and analysis
To analyze the data, Ametek VTI Instruments offers the free EXLab Express software, which provides a spreadsheet-like channel configuration mode to configure channels for voltage and temperature measurements. During the acquisition process, data can be monitored in a variety of ways. The acquired data can then be replayed with EXLab Express or exported to other software for further analysis.
