Pepper Computer RS232, RS485 user manual SM-PT100 Schematic Diagram

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

5.2.5 Functional Description

Figure 5.2.5.1: SM-PT100 Schematic Diagram

User Interface

PT100 Sensor , 4-wire Input

RL	CUR
SUPPLY LINE
400 μA	IN-	Multiplexer
SENSE LINE
SENSE LINE	IN+

400μA

SUPPLY LINE

System Interface

Impedance Converter A/D Converter

Serial

I/O

LED

Driver

System

Interface

RL

AGND

The SM-PT100 has provision for 4 sets of 4-wire PT100 sensors driven by an on-board generated 400μA constant current source. The differential analog input consists of a channel multiplexer, operational amplifier voltage feedback impedance converter and a high-resolution 16-bit delta-sigma converter. 1000V DC system isolation is provided by an optoisolated DC/DC converter while system flexibility is provided by a 256 bytes of serial EEPROM for ID number, production and board-specific calibration data. Two front-panel LEDs show the conversion/calibration activity.

The PT100 is a platinum resistance, which at 0ºC has a resistance of 100Ω and conforms to the international DIN IEC 751 standard for Industrial Platinum Resistance Thermometer Sensors. Two classes A and B exist under this standard with class B experiencing a slightly worse initial error.

Figure 5.2.5.2 Supported Sensor Connections

Red White Red Red White Red Red White Red

Pt 100/ /2 Pt 100/ /3 Pt 100/ /4

5

March 12, 1996 ©1996 PEP Modular Computers GmbH Page 5 - 31