ANALOG DESIGN NOTE Process control instrumentation solutions rose

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ANALOG DESIGN NOTE Process control instrumentation solutions rose

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Instrumentation Electronics Juncture
ANALOG DESIGN NOTE
Process control instrumentation solutions rose 1970s/1980s revolution electronics. From that endeavor well-known instrumentation amplifier came into existence. Structures like three-op design, followed two-op version were built discretely with resistors amps. This solution later made available integrated chip. seem that things haven't changed much since then, digital revolution, that just coming into own, encroaching that traditional analog territory. Instrumentation amplifiers good gaining differential input signals rejecting common mode noise, fall short when there multiple sensor inputs that need integrated into system. instance, pressure sensor load cell require instrumentation amplifier change their differential output signal into single voltage. often these systems need temperature data calibration. This temperature data acquired through separate signal path. alternative having separate signal paths single-ended input/output Programmable Gain Amplifier (PGA). With this device, signal subtraction, common mode noise rejection some filtering differential input signal performed inside microcontroller. also allows multiple input channels, which configurable using SPIport. large number sensors configured inputs. example shown Figure
ADN002
type resistive sensor bridge, shown Figure primarily used sense pressure, temperature load. external converter easily used convert difference voltage from these resistor bridge sensors usable digital words. block diagram Microchip's shown Figure input this device there multiplexer, which allows user interface multiple inputs. This multiplexer directly connected noninverting input wide bandwidth amplifier. programmable closed loop gain this amplifier implemented using on-chip resistor ladder. eight programmable gains are, multiplexer high-speed conversion response combination allows differential input signal quickly sampled converted into their 12-bit digital representation. PIC® microcontroller subtracts signals from CH1. While subtraction signals implemented calculate sensor response, lower frequency common mode noise also eliminated. Although simple measure temperature standalone system without help PGA, variety problems eliminated implementing temperature sensing capability multiplexed environment. main advantages that second signal path microcontroller eliminated, while still maintaining
Pressure Load Sensor Thermistor CS_PGA Pass Filter CS_ADC MCP3201 12-bit
Photo Sensor
MCP6S26
TC1047A Silicon Temp Sensor VREF
PIC® Microcontroller
Figure
device used gain signals from variety sensors, such resistive bridge, temperature sensor, silicon photo sensor silicon temperature sensor. DS21820A Page
2003 Microchip Technology, Inc.
MCP6S21 Single Channel (CH0) MCP6S22 Dual Channel (CH0, CH1) MCP6S26 Channel (CH0 CH5) MCP6S28 Eight Channel (CH0 CH7)
VOUT
Resistor Ladder (RLAD)
Gain Switches
SPILogic
Figure
VREF
Programmable Gain Amplifier (PGA) Block Diagram. internal amplifier that surrounded programmable resistor ladder. This ladder used change gain through port. analog multiplexer precedes noninverting input amplifier allow user configure this device from multiple inputs.
accuracy sensing system. multiplexed versions PGAs MCP6S22 (two channel), MCP6S26 (six channel) MCP6S28 (eight channel). most common sensors temperature measurements thermistor, silicon temperature sensor, thermocouple. Microchip's PGAs best suited interface thermistor silicon temperature sensor. Photo sensors bridge between light electronics. well suited precision applications such scanners, they effectively used position photo sensing applications. multiplexer high-speed conversion response combination allows photo sensor input signal sampled converted analog domain quickly converted digital domain. This photo sensing circuit appropriate signal responses from ~100 kHz. MCP6S2X family that uses precision, wide bandwidth internal amplifier. This precision device only offers excellent offset voltage performance, configurations these sensing circuits easily designed without headaches stability that stand-alone amplifier circuits present designer. Stability with these programmable gain amplifiers been built-in.
more information, access following list references visting www.microchip.com. Recommended References: AN248 AN251 AN865 AN867 Interfacing MCP6S2X PGAs PICmicro® Microcontroller, Ezana Haile, Microchip Technology Inc. Bridge Sensing with MCP6S2X PGAs, Bonnie Baker, Microchip Technology Inc. Sensing Light with Programmable Gain Amplifier, Bonnie Baker, Microchip Technology Inc. Temperature Sensing with Programmable Gain Amplifier, Bonnie Baker, Microchip Technology Inc.
more information, please visit www.microchip.com
Microchip name logo registered trademarks Microchip Technology Inc. U.S.A. other countries. PICmicro registered trademarks Microchip Technology Inc. U.S.A. other countries. trademark Motorola. 2003 Microchip Technology Inc. 9/2003
DS21820A Page
2003 Microchip Technology, Inc.

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