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3064-8/HLSP Certificate IV in Audiometry - Equipment V1i
Acknowledgments
TAFE NSW - Community Services, Health, Tourism and Recreation Curriculum Centre would like to acknowledge the support and assistance of the following people in the production of this resource package:
Writer:
Gloria Armstrong
Audiometrist
Clinical Practice and TAFE NSW
Project Manager:
Gary Wood
Program Manager
Health and Life Sciences Programs
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© 2004, TAFE NSW
3064-8/HLSP Certificate IV in Audiometry - Equipment V11
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3064-8/HLSP Certificate IV in Audiometry - Equipment V11
TABLE OF CONTENTS
General Introduction To This Learning Resource
Module Overview
Module Learning Outcomes
Module Organization
Learning outcome 1
Checking and maintaining audiometric equipment - Audiometer
Practical – 1 hour
Learning outcome 2
Maintenance and calibration of the Tympanometer
Summary
Practical – 1 hour
3064-8/HLSP Certificate IV in Audiometry - Equipment V11
General Introduction To This Learning Resource
This learning resource introduces some of the equipment you may use when performing clinical hearing assessment. This is one of the recurring themes in the audiometry units of competency that are aligned to the Certificate IV in Audiometry HLT41302, which is a qualification of the Health Training Package HLT02. The units of competency that include the theme of Equipment are;
HLTAU1A - Conduct screening hearing tests for children
HLTAU2A - Conduct screening hearing tests for adults
HLTAU3A – Conduct hearing assessment
HLTAU4A – Dispense hearing devices
Equipment is part of the required knowledge that underpins the development of competence. Some equipment is fundamental to the audiometry clinic, some items are optional. The type of equipment you will be regularly using will depend on the situation in which you will be performing audiometry. It is worthwhile to have some knowledge of the more widely used apparatus.
Whilst using this learning resource it may also be necessary for you to access resources at your TAFE college or library. These resources may include computer facilities and software, library material and videos. The resources are listed under the heading Suggested Learning Resources for this learning resource.
This learning resource is designed to complement your class or individual learning activities. You should use this resource as a guide to identify areas of learning.
Module Overview
The purpose of this module is to provide you with basic knowledge about the
type of equipment you will come in contact with as you progress to the practicum
elements of this course. By understanding basic maintenance procedures and implementing routine equipment checks, the clinician helps ensure the validity of the test results. In this module the two most fundamental pieces of equipment are discussed however, it is worth noting that there are a significant number of other types of equipment peculiar to specific clinical situations. Each of the two learning outcomes will relate to a specific piece of equipment and at the end of each section there will be some assessment of the student’s competence.
Module Learning Outcomes
At the end of this module you will be able to;
- Perform biological calibration of an audiometer.
- Examine audiometer for faults.
- Assess and implement strategies to correct equipment failure.
- Perform biological calibration of a tympanometer.
- Examine tympanometer for faults.
- Implement strategies to correct equipment failure.
Module Organization
There are two learning outcomes for the module, Equipment. Each learning outcome addresses a different item of basic equipment that the student needs to know about in order to perform clinical audiometric assessment with surety. The contents are grouped into the following topics;
Learning Outcome 1
Check and maintain audiometric equipment - Audiometer
Learning Outcome 2
Biological calibration and maintenance of the Tympanometer
Learning outcome 1
Check and maintain audiometric equipment - Audiometer
Assessment criteria:
You will have achieved this learning outcome when you can;
- Perform biological calibration of an audiometer.
- Examine audiometer for faults.
- Assess and implement strategies to correct equipment failure.
To complete this topic you will need
Access to an audiometry laboratory or equivalent clinical environment to complete the practical component.
Checking and maintaining audiometric equipment - Audiometer
Recommended Time - 5 hrs
Introduction
Maintaining test equipment is essential if the reliability and validity of test results is to be ensured. Usually a technician will repair any faults with equipment however the clinician plays a major role in ensuring the maintenance and daily care of clinical apparatus.
What is an audiometer?
This piece of equipment has been discussed from time to time - just exactly what is
an audiometer? We know it is an instrument for assessing a person’s hearing levels. Most audiometers can be used to test via air conduction and bone conduction methods. Some audiometers have functions for testing speech discrimination and reception levels. Some can be set to administer hearing assessment automatically as well as manually.
An audiometer consists of an audio oscillator which enables the instrument to generate pure tones at different frequencies, (usually between 250Hz to 8000Hz). An amplifier is also included to allow variation in the loudness levels for each tone presented. Most audiometers range in amplitude from -10dB to 110dB.
On the audiometer you will have noticed the decibel (or amplitude) control and the frequency control. There will also be an on-off switch, usually on the side or back section of the audiometer and an interrupter (or tone presenter) switch. These controls are on all audiometers and, apart from these basic functions; audiometers will vary from model to model.
For those audiometers whose amplitude range is not as high as 110dB, there may be an output switch that, when activated, allows an additional increase in amplitude of 10 - 20dB if required. Some interrupter switches have the ability to present the tone in a ‘pulsed tone’, (warble), as well as a single tone burst. If the audiometer has the functionality to test both air and bone conduction there will be a switch or button enabling the clinician to change between either modes of testing. A single channel audiometer has a switch to change the test ear from left side to right.
Diagnostic audiometers will have ‘masking noise’ available, so there will be an attenuator to activate the masking noise and vary the level of presentation. On some audiometers the switch marked ‘reverse’ will need to be turned on for the masking noise to be heard continuously in the non-test ear. This same switch may be used with speech audiometry. Some audiometers have a microphone allowing you to speak to the client through the earphones. There will be a ‘talk over’ or ‘talk forward’ switch which, when pressed, will activate the ‘talk forward’ microphone. A VU meter will be present on machines with speech audiometry facilities. This is a glass cased needle meter which tracks the volume of the speech presentation, (pre-recorded tape, CD, or by using live voice) through the microphone to the client.
A panel light display may be present on some audiometers. Usually a light will indicate when a tone is being presented (this will pulsate with a pulsed tone presentation). When the client response button is pressed a light will appear on the audiometer for each response made by the client. If the ‘reverse’ button is activated, a red continuous light will be activated until it is cancelled by the operator.
Some audiometers may have only the basic functions and some may have more than are mentioned. Becoming familiar with all the controls on available equipment is important. This allows the clinician to achieve accurate test outcomes using the most appropriate types of tests required.
Definition of calibration
The Macquarie Dictionary describes the word calibrate as “to check the accuracy of any instrument”. Calibration therefore is described as “the act or process of calibrating”. In Martin’s “Introduction to Audiology” calibration is explained as “The electro-acoustic or psycho-acoustic determination that an audiometer is performing properly in terms of its acoustic output, attenuator linearity, frequency accuracy, harmonic distortion, and so on.” (Martin, 1997: 108). So when we send off an audiometer for calibration, the technician will be checking the accuracy of the machine and judging this accuracy against a previously defined standard. In most cases, for Australian audiometry, this standard will be the International Standard Organisation (ISO).
The audiometer is used to test hearing thresholds in the measure known as Hearing Level (HL) or Hearing Threshold Level (HTL). The letters HL or HTL will often be seen on the decibel dial of the audiometer.
Do you remember the curve showing audiometric zero? This curve represents the average sensitivity of normally hearing adults to the frequencies shown on the audiogram. This curve is represented by 0dB on the audiogram and is called HL or HTL.
The aim of calibration is to set the audiometer at the level that is audiometric zero for each frequency.
Activity 1.1
Define dBHTL (dBHL) and state the comparison between dBHTL and dBSPL.
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The comparison between dBHTL and dBSPL is as follows:
Frequency / Decibels HTL / Decibels SPL250Hz
500Hz
1000Hz
2000Hz
4000Hz
8000Hz
Comments on Activity 1.1
When we test an individual’s hearing we relate the measure of intensity needed to dBHTL or dBHL. These terms are synonymous and represent, Decibels Hearing Threshold Level or Decibels Hearing Level. These are in turn related to dBSPL Decibels Sound Pressure Level.
Decibels Hearing Threshold Level is the amount of sound in dBSPL that is needed by a majority of young people with no history of hearing problems (otologically normal) to only just hear a presentation tone at a particular frequency. That level of dBSPL becomes 0dBHTL, which is called audiometric zero. For example, at 1000Hz the majority needed 7.5dBSPL to just hear that sound, so at 1000Hz 0dBHTL=7.5dBSPL.
On average we need more pressure/intensity to hear the lower frequencies and the higher frequencies. In other words, our ears are more sensitive at the mid range. So the comparison between dBHTL and dBSPL is as follows;
Frequency / Decibels HTL / Decibels SPL250Hz / 0 / 26.5
500Hz / 0 / 13.5
1000Hz / 0 / 7.5
2000Hz / 0 / 11.0
4000Hz / 0 / 10.5
8000Hz / 0 / 13.0
The steps for biological calibration
A technician is able to calibrate the audiometer to ISO standards whenever it is sent for this service. There are some things the clinician can do on a regular basis to ensure the good working condition of the audiometer.
When setting up the audiometer each day some standard practices need be observed. Clean the headphones with appropriate wipes and ensure all leads are plugged into the correct place on the patch plate and/or directly into the audiometer. Ensure the tones can be heard through the earphones and bone conductor with the correct correlation.
In an earlier unit the AS/NZS 1269 Standards for workplace audiometry were discussed including what is required for a ‘daily listening check’ of the audiometer.
Activity 1.2
Describe the steps that might be included in a ‘daily listening check’ (or ‘biological calibration’).
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Comments on Activity 1.2
The steps involved in a full daily listening check are;
- Checking earphone cushions for hardened rubber or cracks.
This involves inspecting the cushions on the earphones and feeling them for cracks and hardness. If the cushions are not in good condition, extra ambient noise may seep in through the earphones
- Checking the tension of the headband for the earphones and that all leads are untangled and straightened.
If the headband on the earphones is too loose ambient noise may seep in, or if the band is too tight the testing will be very uncomfortable for the client. When leads are tangled potential problems may occur with the tones being sent through to the headphones. There is a risk of creating an unprofessional appearance if the audiometric equipment is untidy.
- Checking for loose dials and/or clicks when turning the dials on the audiometer.
When turning the dials or pressing the buttons on the audiometer, no sound, except the pure tone being presented, should be passed through to the earphones. If clicks can be heard from the dials by the client, this could give clues as to when the tones are being presented resulting in an unreliable test.
- Checking that the sound through the earphones is free of static or noise due to faulty leads. Turn the attenuator dial to 40 dB at 1000 Hz and listen to the tone while twisting the leads of each earphone separately.
Having static in the earphones can indicate a fault in the audiometer and will be disturbing for the client when being tested. They may be confused as to what noise they are meant to be listening for and respond to sounds other than pure tones.
- Checking for gross linearity at 1000 Hz by setting the attenuator at 10 dB and then increasing it in 10 dB steps up to 90 dB. Listener should check that the increases in loudness are roughly equivalent from one 10dB increment to the next. This should be done for each earphone.
If the decibel level does not increase in loudness in even steps there is a fault with the audiometer and it should be serviced immediately. Any testing with an audiometer that has gross linearity problems will be unreliable.
- Checking for 'cross-talk'. This is done by positioning one only earphone up to the ear and presenting a tone through the OTHER earphone. No sound should be heard in the one held to the ear. Repeat procedure for opposite earphone.
If sound is leaking from one earphone to the other, the clinician cannot be sure which ear is actually being tested. If this fault is detected, arrangements for the audiometer to be repaired must be made immediately.
- Subjective calibration check established by assessing the tester’s own thresholds.
The clinician need have their own hearing checked regularly and know what the levels are. A daily listening check to ensure the audiometer is within 10dB of normal levels at every frequency is standard practice. If the subjective test fails these criteria the audiometer cannot be used and must be sent off for calibration and repair.
Activity 1.3
Look at the audiometer you have access to in your clinical practise placement. The controls and functions should be more familiar now. Answer the following questions;
1.What is the dB limit at 1000Hz for air conduction on the audiometer?
- What is the dB limit at 500Hz for bone conduction on the audiometer?
- How many channels does the audiometer have?
4.What is a ‘pulsed tone’ used for?
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Maintenance of equipment
Carrying out biological calibration on the audiometer goes a long way in ensuring its good working condition. However other important factors must be taken into consideration. Yearly calibration is vital for reliable and valid results to be attained while testing. In fact if a test is carried out on a machine that is out of calibration date, the results CANNOT be accepted. This is particularly important if carrying out any audiometry for compensation or pre-placement medicals.
When a machine is sent for calibration it must be packaged securely, with all leads, earphones and bone conductor pieces included. Wrap each piece of equipment in bubble wrap or foam and pack in a box if the audiometer does not have its own padded travel case. The box must then be marked ‘HANDLE WITH CARE’ or ‘FRAGILE’. If transporting the machine to the technician personally place the box in the car and secure it with a seatbelt.
When the audiometer returns from the calibration centre, check all the pieces have been returned with it. Included with the machine should be a calibration certificate outlining all the frequencies checked and a calibration sticker indicating the next due date for calibration.
It is important to remember when caring for the audiometer and ensuring its reliability to always keep the same earphones and bone conductor with the audiometer. It may be tempting to swap earphones and bone conductors between machines in a clinic where a number of audiometers are available - especially if a fault is found. This is not allowable. Each machine is calibrated to the earphones and bone conductor that come with it. The audiometer cannot therefore be used with a different set unless it is recalibrated for that set. Under no circumstances swap sets as results will be invalid.
Activity 1.4
If possible, visit a centre where audiometers are calibrated and obtain permission to watch the calibration process. Note how the technician checks for faults and what they are looking for when calibrating each frequency.