Lesson Notes By Weeks and Term v4 - SHS 3
DIAGNOSTIC DEVICE
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
DIAGNOSTIC DEVICE
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Biomedical Science
Class: SHS 3
Term: 2nd Term
Week: 3
Grade code: 2.3.1.LI.3
Strand code: 3
Sub-strand code: 1
Content standard code: 2.3.1.CS.1
Indicator code: 2.3.1.LI.3
Theme: BIOMEDICAL INTERVENTION
Subtheme: DIAGNOSTIC DEVICE
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
This lesson introduces the fundamental principles of bioinstrumentation, which is the science behind how medical diagnostic devices work. In Ghana today, devices like blood glucose monitors, digital blood pressure machines, and electronic thermometers are becoming common in our homes, pharmacies, and CHPS compounds. Understanding how they are built is not just for scientists; it helps us appreciate the technology, use it correctly, and even identify when it might be faulty. We will break down a typical diagnostic device into its core components and see how it converts a biological signal (like sugar in our blood) into a number we can read and understand.
What is Bioinstrumentation? Bioinstrumentation is a field of science and engineering that involves developing and using medical instruments to measure, record, and analyse biological signals from the human body. Simply put, it's the technology that allows us to "see" what's happening inside our bodies without cutting them open. These measurements help doctors and nurses diagnose diseases, monitor a patient's condition, and guide treatment. The Core Principles: The Bioinstrumentation Block Diagram Almost every electronic diagnostic device, from the simplest to the most complex, is built on a set of common principles. We can represent this with a simple block diagram:
Measurand → Transducer/Sensor → Signal Conditioning → Signal Processor → Output/Display
Let's break down each block step-by-step. Measurand Definition: The measurand is the physical, chemical, or biological quantity, property, or condition that the system measures. It is the specific thing in the body we want to know about. Examples: Body temperature (°C) Blood pressure (mmHg) Glucose concentration in blood (mmol/L) Heart rate (beats per minute) Oxygen saturation in blood (%) Electrical activity of the heart (ECG) Transducer / Sensor Definition: A transducer is a device that converts one form of energy into another. In bioinstrumentation, the transducer is the "sensor" part that detects the measurand and converts it into a usable electrical signal (like voltage, current, or resistance). This is the most critical part of the device. How it works: The transducer interacts directly with the body or a body sample (like blood). Examples: Thermistor: Used in digital thermometers. It's a resistor whose resistance changes predictably with temperature. So, it converts heat energy (measurand) into electrical resistance (signal). Electrochemical Sensor: Used in a glucometer test strip. It uses an enzyme (like glucose oxidase) to cause a chemical reaction with glucose. This reaction produces a tiny electrical current that is proportional to the amount of glucose. It converts chemical energy into electrical current. Pressure Sensor (Strain Gauge): Used in digital blood pressure monitors. The pressure from the cuff squeezes the sensor, changing its electrical resistance. It converts mechanical pressure into an electrical signal. Signal Conditioning Definition: The electrical signal from the transducer is often very weak, "noisy" (mixed with unwanted signals), and not in the right format for the next stage. The signal conditioning circuit "cleans up" and prepares the signal. Key Functions: Amplification: The signal is made much stronger (larger). Imagine someone whispering (the raw signal); the amplifier is like a microphone and speaker system that makes the whisper loud and clear. Filtering: Unwanted noise is removed. This is like using a filter on a radio to tune into one station clearly and block out the static from other stations. Analog-to-Digital Conversion (ADC): Most biological signals are analog (continuous, like a wave). Modern devices use digital processors (like mini-computers). The ADC converts the smooth analog signal into a series of digital numbers (0s and 1s) that the processor can understand. Signal Processor Definition: This is the "brain" of the diagnostic device. It is usually a small computer chip called a microprocessor. Function: It takes the clean, digital signal from the conditioning circuit and performs calculations on it using a pre-programmed algorithm (a set of mathematical instructions). This algorithm converts the electrical value into a clinically meaningful measurement. Example in a Glucometer: The processor receives a digital value representing the electrical current from the test strip. The algorithm inside it knows that "X amount of current = Y concentration of glucose". It does this calculation and determines the final blood sugar reading (e.g., 6.5 mmol/L). Output / Display Definition: This is the final component that presents the processed information to the user (the patient or healthcare worker). Function: It communicates the result in a human-readable format. Examples: LCD Screen: Shows numbers (e.g., "120/80 mmHg" for blood pressure). Beep/Sound: Indicates that the measurement is complete or if there is an error. Light (LED): A green light might mean a normal result, while a red light indicates a high or low reading. Printed Report: More complex machines like ECGs print the results on paper.