Know-how: Current Sensing & MeasurementMichela Radice
Current sensing and measurement is a common need in many different test applications, and it is especially required in automotive in the validation and testing of ADAS (Advanced Driver Assistance Systems) like infotainment devices, instrument panel clusters, etc. and in Electric Vehicle testing, specifically for Battery Management Systems testing.
A typical use case is represented by DUT (Device Under Test) power on and current consumption: in this scenario the DUT – either the infotainment head unit, or the instrument panel cluster – needs to be connected to the power supply input, and at the same time the ignition switch must be closed, so that the DUT stand-by and nominal supply current is measured. The measurement is usually taken on demand, using a trigger signal. The required resolution depends on the current range, so automatic scaling is highly recommended to achieve maximum resolution.
Flexmedia XM CSENS25A2 module is a versatile tool specifically designed to measure current flow up to 25A; at the same time, voltage is measured on both input and output pins. It is designed to take on-demand triggered current measurement. Selecting the bit resolution and the number of acquisitions to average, allows more precision, but requires more time for the measurement.
This module is capable of DC power switching and current sensing, and features four scales of current measurement (250µA, 25mA, 2.5A, 25A) that are automatically selected for optimal resolution. Moreover, it includes input and output voltage measurement (0.5V to 32V voltage range). Additional features include over-temperature and over-current protections (max 25A), an external opto-isolated trigger (3V to 6V) and an auxiliary solid-state relay for ignition input (max 100mA for ON-state, max 50V for OFF-state).
When the module is not measuring, the current flows in the 25A path (provided that the internal main switch is on). Then, when the measure command is sent, it measures in the 25A range current and, only if the current value is below a threshold, the module proceeds in measuring again in the lower current range of 2.5A, then again 25mA, etc.
The 25A path is controlled by an active chipset, with multiple protections.
It is possible to setup a maximum expected current (in the range 1A – 25A) within a maximum “in-rush timeout” (in the range 1ms – 1s): at power on, the current can exceed the maximum expected value, within the maximum time interval specified by the in-rush time, without triggering the overcurrent protection.
As an additional feature, two pins of a solid-state relay are available to act as a switch: when AUX Relay is activated, these pins are short circuited.
Each Current Sensing & Measurement module is controlled by an external host. Power is delivered via Power-over-Ethernet (PoE), according to IEEE 802.3af standard.