FEATURE Industry 4.0
Compact software-confi gurable battery-powered precision
calibrator that packs a punch By Konrad Scheuer, Senior Principal, and Sean Long, Executive Director of applications for the Industrial and Healthcare Business Unit, at Maxim Integrated (now Analog Devices)
I
ndustrial analogue I/O modules are used to transmit and receive precise, low-level voltage and current signals to and from sensors and actuators situated on the factory fl oor. Like all electronic devices, repeated use and changing environmental conditions over extended time periods cause their performance to deteriorate, requiring periodic calibration to ensure that they continue operating to a predetermined way.
Indeed, in many industries, periodic calibration is a regulatory requirement, necessitating a trained technician, who will use diff erent instruments that can be heavy and cumbersome. Calibrating all channel types within an I/O module requires a voltage source and meter, a current source and meter, and a source that can simulate the voltage outputs from diff erent types of thermocouples and RTDs used by I/O channels measuring temperature – all can add to the number of equipment a technician needs to transport to the wiring cabinet. Precision instruments that incorporate all features are available, but are also large, heavy and expensive.
Compact calibrator The MAXREFDES183# reference design, shown in Figure 1, is a software- confi gurable battery-powered precision calibrator that is compatible with common industrial analogue input and output and voltage and current ranges. Compared with bulky desktop calibrators, this calibrator measures only 108mm × 83mm × 36mm and weighs just 283g. The MAXREFDES183# incorporates multiple design techniques to maximise thermal performance and improve the overall accuracy and stability of the calibrator. Temperature monitoring is provided by two instances of a low power I2
C temperature sensor, the MAX31875, with accuracy of ±1°C between 0°C and 70°C.
24 June 2022 | Automation
The calibrator is powered by two 3.6V, 3500mAh capacity Li-Ion batteries. A fuel gauge monitors and manages battery states including voltage, current and temperature, and uses external high-side FETs to guard against over-/under- voltage, overcurrent, short circuit, temperature extremes, overcharging and internal self- discharge. Charging prescription ensures that the batteries operate under safe conditions, prolonging life between recharging. The IC automatically compensates for cell ageing, temperature and discharge rate, and provides accurate state of charge in milliampere- hours or percentage over a wide range of operating conditions. A thermistor is used to measure battery temperature. A fl yback converter boosts the USB voltage (5V nominal) to the battery pack voltage (nominally 7.2V), providing voltage input to the multiple DC-to-DC converters that generate the voltage rails required to power other components. The MAXREFDES183# consumes 110mA (typical), providing up to 31 hours of normal usage between battery charging cycles.
The accuracy of the reference design is within 0.01% FSR at room temperature (25°C).
While accuracy over temperature is important, calibration equipment is usually used and stored in environments that have a relatively stable temperature. Therefore, it is also important that they exhibit a high degree of repeatability over longer time intervals at a fi xed temperature.
Setting up Even precision calibrators require periodic calibration. The MAXREFDES183# includes a preprogrammed calibration
Figure 1: The MAXREFDES183# reference design is a software-configurable battery-powered precision calibrator, compatible with common industrial analogue inputs and outputs, and voltage and current ranges
routine that clearly explains how external meters and sources should be connected, and provides feedback to the user, interpreting results to determine if they are within acceptable boundaries. MAXREFDES183# 3D printer fi les can be downloaded to create an enclosure for the calibrator.
Hence, the MAXREFDES183# precision calibrator reference design demonstrates a lightweight, ultra-portable, battery- powered calibrator with the functionality, performance and accuracy of much larger, heavier and more expensive solutions. Potential applications for products based on this design include laboratory equipment calibration, adjustment of industrial control equipment and fi eld calibration of smart sensors and actuators for Industry 4.0 and beyond.
CONTACT:
Analog Devices
www.analog.com
automationmagazine.co.uk
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