maxPAC Hardware Reference Guide
Metso Automation MAX Controls Inc. • 277596 •
2-4
Module Operation
This microprocessor-based module supports up to 16 isolated high level
inputs. A sigma delta A/D and precision reference is provided for each pair
of inputs. The A/D reads the voltage generated by the selected input and
converts the differential measurement to a 15-bit plus sign binary value
representing the voltage input, which is read by the microcontroller. The
microcontroller initiates the conversion and waits for the conversion to
complete.
The digital filter in the oversampling A/D provides excellent 50/60 Hz
normal mode rejection. Prior to starting each conversion, the microcontroller
selects one of the two input channels by means of two solid-state, optically
coupled relays. The two inputs are multiplexed with optical relays to provide
channel to channel isolation. Immediately following each measurement,
open input and over range conditions are checked.
A separate DC/DC converter provides isolated power to each A/D converter
measuring circuit. Communication between the microcontroller and each
A/D is serial at 100kHz. A separate group of optical isolators provide the
isolation between each A/D and the serial logic circuits. The microprocessor
provides the input data to the DPU on demand via the bus FPGA. The FPGA
provides the I/O bus interface logic; its program is loaded from the FLASH
on power up.
Module calibration is done automatically at power up following startup
diagnostics. Calibration is repeated periodically online to compensate for
temperature effects.
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