Pepper Computer RS232, RS485 user manual SM-THERM Schematic Diagram

Chapter 5 Analog Modules SMART I/O User’s Manual

5.3.5 Functional Description

Figure 5.3.5.1: SM-THERM Schematic Diagram

LED

Driver

Thermo Sensor

SHIELD LINE	AGND	Multiplexer
SENSE LINE	IN+
SENSE LINE	IN-
	SUPPLY/SENSE LINE
	TMP+
	TMP-
	SUPPLY/SENSE LINE

External PT100 Sensor, 2-wire Cold Junction Input

Impedance Converter

A/D Converter

Serial

I/O

System

Interface

The SM-THERM allows four sets of three-wire thermocouples to be con- nected together with one additional PT100 element used as a cold junction point reference. The differential analog input consists of a channel multi- plexer, operational amplifier voltage feedback impedance converter and a high-resolution 16-bit delta-sigma converter. 1000V system isolation is provided by an optoisolated DC/DC converter while system flexibility is provided by 256-bytes of serial EEPROM for ID number, production and board specific calibration data. Two front-panel LEDs show the conversion/ calibration activity.

In principle any thermocouple conforming to the DIN43710 or IEC584 specifications can be connected. Sensor breakdown recognition is performed by the software which also caters for and corrects absolute temperature readings with a connected cold junction point (PT100).

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March 12, 1996 ©1996 PEP Modular Computers GmbH Page 5 - 61