Note the following details of the code protection feature on Microchip devices:
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INTRODUCTION
This chapter contains general information that will be useful to know before using the
PT100 RTD Evaluation Board. Items discussed in this chapter include:
• Document Layout
• Conventions Used in this Guide
• Recommended Reading
• The Microchip Web Site
• Customer Support
• Document Revision History
DOCUMENT LAYOUT
This document describes how to use the PT100 RTD Evaluation Board as a
development tool. The manual layout is as follows:
• Chapter 1. “Product Overview” – Important info rmation about the PT100 RTD
Evaluation Board.
• Chapter 2. “Installation and Operation” – This chapter includes a detailed
description of each function of the demo board and instructions for how to begin
using the board.
• Appendix A. “Schematic and Layouts” – Shows the schematic and layout
diagrams for the PT100 RTD Evaluation Board.
• Appendix B. “Bill Of Materials (BOM)” – Lists the parts used to build the PT100
RTD Evaluation Board.
This user's guide describes how to use the PT100 RTD Evaluation Board. The
following Microchip documents are available on our web site ( www.microchip.com) and
recommended as supplemental reference resources.
MCP6S26 Data Sheet, “Single-Ended, Rail-toRail I/O, Low Gain PGA“ (DS21117)
This data sheet provides detailed information regarding the MCP6S26 device.
MCP3301 Data Sheet, “13-Bit Differential Inp ut, Low Power A/D Con ver ter w/SPI
Serial Interface” (DS21700)
This data sheet provides detailed information regarding the MCP3301 device.
MCP602X Data Sheet, “Rail-to-Rail Input/Output, 10 MHz Op Amps“ (DS21685)
This data sheet provides detailed information regarding the MCP602X devices.
MCP41010 Data Sheet, “Single/Dual Digital Potentiometer with SPI Interface“
(DS11195)
This data sheet provides detailed information regarding the MCP41XXX devices.
PIC18F2455/2550/4455/4550 Data Sheet, “28/40/44-Pin, High-Performance,
Enhanced Flash, USB Microcontrollers with nanoWatt Technology“ (DS39632)
This data sheet provides detailed information regarding the
PIC18F2455/2550/4455/4550 devices.
TC1070/TC1071/TC1187 Data Sheet, “50mA, 100mA, and 150mA Adjustable
CMOS LDOs w/Shutdown“ (DS21353)
This data sheet provides detailed information regarding the TC1070/TC1071/TC1187
devices.
Preface
THE MICROCHIP WEB SITE
Microchip provides online support via our web site at www.microchip.com. This web
site is used as a means to make files and information easily available to customers.
Accessible by using your favorite internet browser, the web site co ntains the following
information:
• Product Support – Data sheets and errata, application notes and sample
programs, design resources, user’s guides and hardware support documents,
latest software releases and archived software
• General Technical Support – Frequently Asked Questions (FAQs), technical
support requests, online discussion groups, Microchip consultant program
member listing
• Business of Microchip – Product selector and ordering guides, latest Microchip
press releases, listing of seminars and events, listings of Microchip sales offices,
distributors and factory representatives
Users of Microchip products can receive assistance through several channels:
• Distributor or Representative
• Local Sales Office
• Field Application Engineer (FAE)
• Technical Support
• Development Systems Information Line
Customers should contact their distributor, representative or field application engineer
for support. Local sales offices are also available to help customers. A listing of sales
offices and locations is included in the back of this document.
Technical support is available through the web site at: http://support.microchip.com
DOCUMENT REVISION HISTORY
Revision B (December 2007)
• Changed Information Related to the GUI.
• Updated Figure 2-3 and Figure 2-6.
• Updated Section 2.3.2 “Software Setup”.
• Add disclaimer to Bill of Materials regarding RoHS-Compliant part numbers.
This chapter provides an overview of the PT100 RTD Evaluation Board and covers the
following topics:
• What is the PT100 RTD Evaluation Board?
• What the PT100 RTD Evaluation Board kit includes.
1.2WHAT IS THE PT100 RTD EVALUATION BOARD?
The PT100 RTD Evaluation Board demonstrates how to bias a Resistive T emperature
Detector (RTD) and accurately measure temperature. Up to two RTDs can be
connected. The RTDs are biased using const ant current source and the outpu t voltage
is scaled using a difference amplifier. In addition to the difference amplifier, a multiple
input channel Programmable Gain Amplifier (PGA) MCP6S26 is used to digita lly switch
between RTDs and increase the scale up to 32 times.
The output of the difference amplifier is connected to a 12-bit differenti al
Analog-to-Digital Converter (ADC) MCP3301. The ADC outputs serial data to the
PIC18F2550 using a Serial Peripheral Interface (SPI). The dat a is transmitted to a PC
using a USB interface.
A PC Software Graphical User Interface (GUI) is used to acquire the data. The acquired
data is graphed as a real-time stripchart display. In addition, the user can select input
channels, acquisition interval, and stripchart display buffer size.
1.3WHAT THE PT100 RTD EVALUATION BOARD KIT INCLUDES
This PT100 RTD Evaluation Board Kit includes:
• The PT100 RTD Evaluation Board (102-00096)
• PIC18F2550 Firmware (USB)
• PC Software GUI
• Analog and Interface Products Demonstration Boards CD-ROM (DS21912)
The PT100 RTD Evaluation Board allows the user to evaluate Microchip’s solution to
accurately measure temperature using RTD. When biasing RTDs to measure
temperature, self-heat due to power dissip ation has to be consider ed. R TD resist ance
availability typically ranges from 100Ω to 5,000Ω. In order to measure the output
voltage across the RTD over a wide temperature range, the biasing curr ent has to be
relatively high. This higher current causes more power dissipation through heat and
skews the temperature reading. Microchip’s solution to this challenge is to use the
MCP6S26 Programmable Gain Amplifier (PGA) to increase the sensor dynamic output
range and increase measurement resolution while significantly reducing the biasing
current magnitude.
This board consists of a surface mount RTD to measure the PCB temperature and an
external RTD connector. In addition, the user can connect and measure an external
leaded RTD (2, 3, or 4-Wire) and configure the corresponding jumper to remotely
measure temperature. The multiple input channel PGA adds gain programmability into
the analog circuit. The multiple input channels are used to switch between RTDs and
the gain is used to increase the sensor dynamic range.
The PGA output is connected to a differential amplifier circuit which allows the user to
scale the sensor output. The differential output is digitized using an MCP3301 12-b it
differential analog-to-digit al converter . The data is tran smitted to the PC using the USB
interface. A PC Software Graphical User Interface (GUI) is used to obtain and display
the data in real-time.
PT100 RTD EVALUATION
BOARD USER ’S GUIDE
2.2FEATURES
The PT100 RTD Evaluation Board has the following features:
• A surface mount PT100 RTD
• External (2, 3, or 4-wire) RTD connector
• Gain and input channel programmability using MCP6S26 PGA
This section describes how to quickly configure the PT100 RTD Evaluation Board. A
simplified block diagram of the configuration is provided in Figure 2-1.
The PT100 RTD Evaluation Board uses surface mount RTD to measure
temperature. An external 2, 3, or 4-wire PT100 R TD can also be connected to measure
temperature in remote locations. The RTDs are b iased using a constant current source.
In order to reduce self-heat due to power dissip ation, the current magnitude is relatively
low. The sm all voltage across the RTD is amplified using the MCP6S2 6 PGA. The PGA
allows the user to digitally program the amplifier gain and increase the sensor output
range. The output of the PGA is scaled using a differential amplifier. The differential
amplifier drives a 12-Bit + sign differential ADC, MCP3301. The digital data is read
using PIC18F2550 and transmitted to PC using a USB interface.
2.4.1.1THE RTD BIASING CONSTANT CURRENT SOURCE
The constant current source uses a reference voltage, one amplifier, and a PNP
transistor, as shown in Figure 2-4.
FIGURE 2-4:Constant Current Source.
The amplifier maintains constant voltage at the transistor emitter terminal. Therefore,
the emitter and collector currents are constant. The collector current biases the RTD.
The biasing current can be fine tuned by adjusting the 10 kΩ digital potentiometer using
the GUI. A 100Ω, 0.1% resistor is available for system calibration at 0°C (RTD
resistance at 0°C is 100Ω). This resistor can be jumped using JP1.
When connecting an external PT100 RTD, connect JP2 to External Position.
2.4.1.2RTD SIGNAL CHAIN
The PGA is used to amplify the small voltage across the R TD. The reference inp ut pin
of the PGA is connected to the RTD negative terminal and Channel 0 and Channel 1
are connected to the positive terminals of each RTD. This allows only the voltage
across the sensor to be amplified. The PGA has a gain error of ±1% (max.) for gains
greater than 1 V/V. Refer to the datasheet (DS21685) for details.
The RTD negative terminal and the PGA output are connected to the differential
amplifier. The differential amplifier scales the PGA output. The difference amplifier gain
is shown in Equation 2-1.
EQUATION 2-1:DIFFERENCE AMPLIFIER GAIN
2.4.1.3THE GRAPHICAL USER INTERFACE
The GUI uses the USB port to communicate with the PIC18F2550.
FIGURE 2-6:Hardware Status
When start is clicked, the macro double checks hardware availability before starting
the acquisition.
All user options such as Sampling time, Stripchart buffer size, Digi. Pot Positions,
or PGA Chn/Gain setup can be changed during acquisition.
1D2MA3X786E0LCT-NDPanasonic - SSGMA3X786E0L
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1J2CONN RECEPT MINI USB2.0 5POS Hirose Electronic Co LtdUX60-MB-5ST
1J2USB A Male to Mini USB B 5 pin