Note the following details of the code protection feature on Microchip devices:
•Microchip products meet the specification contained in their particular Microchip Data Sheet.
•Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
•There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
•Microchip is willing to work with the customer who is concerned about the integrity of their code.
•Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
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All documentation becomes dated, and this manual is no exception. Microchip tools and
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(www.microchip.com) to obtain the latest documentation available.
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IDE on-line help.
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 information 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
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 Input, Low Power A/D Converter 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 contains 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
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 Temperature
Detector (RTD) and accurately measure temperature. Up to two RTDs can be
connected. The RTDs are biased using constant current source and the output 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 digitally switch
between RTDs and increase the scale up to 32 times.
The output of the difference amplifier is connected to a 12-bit differential
Analog-to-Digital Converter (ADC) MCP3301. The ADC outputs serial data to the
PIC18F2550 using a Serial Peripheral Interface (SPI). The data is transmitted to a PC
using a USB interface.
A Microsoft
data. The acquired data is stored in an Excel Worksheet and graphed as a real-time
stripchart display. In addition, the user can select input channels, acquisition interval
and stripchart display buffer size.
®
Excel® macro is used as a Graphical User Interface (GUI) to acquire the
1.3WHAT THE PT100 RTD EVALUATION BOARD KIT INCLUDES
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 dissipation has to be considered. RTD resistance
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 current has to be
relatively high. This higher current causes more power dissipation through heat and
skews the temperature reading. Microchp’s solution to this challenge is to use an
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. 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-bit
differential analog-to-digital converter. The data is transmitted to the PC using the USB
interface. A Microsoft Excel-based 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 RTD can also be connected to measure temperature in remote locations. The RTDs are biased using a constant current source. In
order to reduce self-heat due to power dissipation, the current magnitude is relatively
low. The small voltage across the RTD is amplified using the MCP6S26 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 CONSTANT CURRENT SOURCE
The constant current source uses a reference voltage, one amplifier and a PNP
transistor, as shown in Figure 2-4.
V
DD
7kΩ
SPI
3
10 kΩ Digital
Potentiometer
R
WIRE
V
REF
MCP6022
PNP Transistor
RTD (100Ω @°C)
1kΩ
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.
The PGA is used to amplify the small voltage across the RTD. The reference input 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
2R
×
F
------------------------ RG20Ω+
Where:
R
= 10 kΩ
F
R
= 10 kΩ Digital Potentiometer
G
2.4.1.3THE GUI
+=
G1
⎛⎞
⎝⎠
The GUI uses a Microsoft Excel-based macro to open the USB port and communicate
with the PIC18F2550. When the file is opened, the macro checks hardware status. The
status display indicates hardware status as shown in Figure 2-6.
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.