Page 1: Introduction

Introduction to Module WM 273

• Topic: Instrumentation & Control

• Instructor: Matt Sokola

• Important Note: Use PowerPoint presentation mode for optimal viewing, especially from Slide 8 onwards.

Page 2: Lecture Overview

Lecture 2.b Topics

• Basic Principles

• Design Guidelines

• Example: Temperature sensor conditioning from 0 to 5 V

• Related Concept: Operational Amplifiers for Signal Conditioning

Page 3: Signal Conditioning

Aims of Analogue Conditioning

• Main Objective: Match the sensor’s output to the next stage of electronics, focusing on:

  • Range of signals

  • Offset of signals

• Other Functions:

  • Prevent loading of the sensor

  • Range adjustment/tuning

  • Flexible offset elimination

  • Filtering out signal spikes

  • Linearizing non-linear sensor outputs

  • Alerting about dangerously high or low levels

Page 4: Design Guidelines

Key Considerations for Analog Signal-Conditioning

• Sensor selection from market products

• Design conditioning circuit based on sensor output to produce recognizable ranges for control and monitoring systems.

• Overview of basic design guidelines to be discussed.

Page 5: Guidelines Overview

Models for Measurement and Signal-Conditioning Tasks

1. Identify measurement objectives

2. Select sensor based on output type

3. Design signal conditioning circuit appropriately

Page 6: Fundamental Steps

Steps for Analog Signal Conditioning

1. Define Measurement Objectives:

   • Parameters include: pressure, temperature, flow, current, voltage, resistance, etc.

   • Consider range, accuracy, linearity, speed of changes, and noise issues.

2. Select Sensor:

   • Based on output type (resistance, voltage), transfer function, response time, range, and power.

3. Design Analog Signal Conditioning:

   • Define input/output range, input/output impedances.

Page 7: Instrumentation Amplifiers

Example Scenario

• Sensor Output: Voltage range 20 to 250 mV for temperature 0 to 115 °C.

• Task: Develop an analog conditioning circuit to convert to 0 to 5 V for D/A conversion.

• Requirement: High input impedance to avoid sensor loading issues.

Page 8: Define Transfer Function

Step 1: Transfer Function

• Use linear equation for voltage relation: y = mx + b

• Calculations:

  • m = 5 / (250 – 20) mV = 21.74

  • V0 = -0.02 x 21.74 = -0.4348

• Options for Amplifier Design:

  • Option 1: Summing amplifier

  • Option 2: Differential amplifier

Page 9: Circuit Structure

Step 3.1: Choose Structure

• Differential amplifier with gain of 21.74

• Input Voltage ranges from 20 mV to 250 mV

• Use options for differential amplifier design.

Page 10: Achieving Required Gain

Step 3.2: Gain Solutions

• Question: Is a 217.4 kΩ resistor available?

• Standard Resistor Values: E12 series

• Four options for achieving gain:

  1. Use a 220k resistor

  2. Series combination of 150k and 68k

  3. Combination of 8.2k and 180k

  4. Combination of 1.8k and 39k

• Recommendation: Option No. 4 to maintain simplicity while achieving near-target gain.

Page 11: Resistor Ratios

Ratios of E12 Resistors

• List of standard resistor values and corresponding ratios for achieving desired gain settings.

Page 12: Simplest Circuit

Circuit Configuration

• Vout Equation: Vout = 21.74 (Vin - 0.02)

• Components: Resistors and input/output voltage references outlined.

Page 13: Setting Reference Voltage

Step 3.3: Setting Reference Offset

• Method to set up 0.02 V offset using supply and resistors as voltage dividers.

• Important Note: Watch for fluctuations in reference voltage related to supply.

Page 14: Using Zener Diode

Alternative Method for Stable Reference Voltage

• Choose a Zener diode for stable low voltage output.

• Calculation steps for R3 and the attenuation ratio with examples using E12 series.

Page 15: Final Circuit and Output

Circuit Summary

• Input: V_in = 250 mV produces approximately 5 V output with detailed component specification.

Page 16: Summary of Operational Amplifiers

Key Points

• Operational amplifier: Fundamental building block for signal processing

• Behavior: Real op-amps approximate ideal behavior up to certain frequency limits (1 kHz to 10 kHz).

• Applications Include:

  • Amplifying current, adjusting voltage, offset adjustment, signal addition/subtraction, integration, and signal comparison for digital outputs.