Isolated Power Modules for Data Acquisition & Control

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A data acquisition (DAQ) system uses a computer to measure and process an electrical or physical parameter such as voltage, current, temperature, force, pressure, flow, sound, etc. A DAQ system consists of sensors, measurement hardware, and a computer or microcontroller unit (MCU) with application-specific software. The sources of these measurements might be located far within a building or across buildings or fields. This note describes using isolated modules to power a DAQ system with protection against faults in field environments.
 

A DAQ interfaces to field sensors in electric meters, gas meters, water meters, heating, ventilation and air conditioning systems, etc. Field sensor outputs are conditioned to match a standard voltage span (i.e. 0-5 VDC) before analog-to-digital conversion (ADC). Digitized data from an ADC can be transmitted via RS-485 or a similar field interface. Field sensors and RS-485 transceivers should use an isolated power source for protection against ground voltage level shifts and electrical faults. Typical electrical isolation voltage ratings start at 1k Vpk and might be specified by compliance standards in certain applications. Additionally, isolated power sources reduce effects from electromagnetic interference (EMI).
 

The MCU in the DAQ system can also calculate control values for a system’s actuator (i.e. motor, damper, valve, press, etc.). Control values are transmitted via RS-485 or similar field interface to a remote digital-to-analog converter (DAC) before reaching the actuator. Components in this output path should also use isolated power sources for protection against electrical faults and reduce effects from EMI.
 

Power sources can be designed with discrete components or can be ready-to-use modules which offer guaranteed performance specifications and reduced time to market. Figure 1 illustrates an example of a DAQ and Control system with AC or DC input power option. The wide 90-528 VAC input range is accommodated by Aimtec AME1, AME2 or AME3 modular converters. DC sources also can power DAQ systems; these sources can range from low voltage batteries to more than 70 VDC in rail systems, generators and other high DC voltage sources. Aimtec DC-DC modular converters such as AM2G-Z with 2:1 or AM2GH-Z with 4:1 input voltage range accommodate voltage fluctuations in DC sources (i.e. AM2GH-Z converters with the input voltage option between 9 and 36 V have a 4:1 input range). Figure 1 also shows ADCs, DACs and MCU operating at 5 VDC and RS-485 transceivers operating at ±5 VDC. These output voltages can vary for systems operating at other unipolar or bipolar bus voltages such as 3.3, 12, 24, ±12 VDC, etc.