The doseBadge and Reader can produce the following metrics as defined in the relevant standards. Some of these are available on the Reader display, others require a printer or the computer software supplied.

When the data is downloaded from the RC:110A Reader unit to the doseBadge software, the following parameters are provided:

L_Aeq

The level which, if maintained constant for the same period as the measurement, would contain the same amount of energy as the fluctuating noise level. “A” weighted and expressed in decibels (dBA). Doubling the energy results in a 3dB change in the L_eq. This is denoted by Q=3. The Threshold used in the calculation of L_AVG (see below) is not used for the calculation of L_Aeq.

For example:

If the noise level in a factory was a constant 85dB and the measurement period was 4  hours, the L_Aeq would be 85dB(A).

L_EP,d

The L_EP,d is the average of the measured L_eq over an eight hour period. The L_EP,d will be lower than the L_eq when the measurement duration is less than eight hours, equal to the L_eq for a measurement of eight hours, and higher than the L_eq for measurements over eight hours.

For example:

If a noise measurement was made for 4 hours and the L_Aeq value was 90dB(A), the L_EP,d value would be calculated to be 87dB(A) as the measurement duration is half the Criterion Time of 8 hours and the exchange rate is 3dB.

L_EX,8h

Under the EU Physical Agents (Noise) Directive which will be introduced in member states of the EU by February 2006, the terminology for the Daily Personal Noise Level or L_EP,d has been changed to be L_EX,8h.  The calculation is the same and the data is calculated from the LAeq and Measurement Duration in the same way as for L_EP,d.

L_AVG

L_AVG is the average Sound Level over the measurement period when the exchange rate (Q) is other than 3dB or where there is a Threshold applied or a Time Weighting applied.

L_AVG is the equivalent of L_eq for exchange rates other than 3dB, for example Q=5. The Threshold value is used during the calculation of L_AVG with any levels below the threshold not being included.

For example:

Assume the threshold level is set to 80dB and the exchange rate is 5dB (which are the settings for OSHA’s Hearing Conservation Amendment). If a one hour measurement was taken in an environment where the noise levels varied between 50dB and 70dB, the sound level would never exceed the threshold level and the instrument would record no value for the L_AVG. If the sound level exceeded the 80dB threshold for only a few seconds, then only these seconds would contribute to the L_AVG giving a level of around 40dB which is much lower than the actual ambient sound levels in the environment.

TWA

The Time Weighted Average is the average of the measured L_AVG over an eight hour period. The TWA will be lower than the L_AVG when the measurement duration is less than eight hours, equal to the L_AVG for a measurement of eight hours, and higher than the L_AVG for measurements over eight hours.

% Dose

A percentage of a fixed dose value based on the criterion level and criterion time. The criterion level and time are set by local standards.

For example, some Regulations may mandate the use of 85dB for 8 hours as the limit for a daily noise exposure. If the noise level was a constant 85dB for 8 hours, this would generate a % Dose of 100%.

Estimated Dose

Estimates the % dose (described above) that would have been received by the wearer if the average level measured had existed for the period defined by the criterion time.

For example, if for a 4 hour measurement the % Dose was 50%, the Estimated Dose would be 100% for the 8 hours of the Criterion Time.

Exposure (Pa5s, Pa5hr)

The noise exposure expressed in linear terms rather than using the logarithmic dB unit or % dose. Expressed in Pascal squared hours (Pa5hr) or Pascal squared seconds (Pa5s).

Estimated Exposure

Estimates the exposure (described above) that would have been received by the wearer if the average level measured had existed for the period defined by the criterion time. Expressed in Pascal squared hours (Pa5hr).

Overload

Indicated when the noise level exceeds the upper design limit of an instrument. In the doseBadge this is set to 130dB(A) Sound Level

Glossary

There are many different standards for noise measurement instruments such as sound level meters, noise dosemeters and acoustic calibrators and these will each have their own specific requirements, tolerances and performance criteria.

In the UK, the requirements for instruments that will be used to measure noise at work are defined in the Noise at Work Regulations ^[1].

This lists the standards that instruments should meet and for personal sound exposure meters, or noise dosemeters, this is given as BS EN 61252:1997^[2].

BS EN 61251:1997^[2] and the corresponding International version IEC 61252:1993^[3] lay out the performance required from a noise dosimeter along with the tolerances that are allowed.

Both of these have a single level of performance that the instrument must meet and as such there are no references to Class or Type.

The Noise at Work regulations [1] state “Your dosimeter should meet the requirements of BS EN 61252:1997. Dosemeters have no type or class number”.

This is in contrast to the standards for sound level meters, IEC 61272:2002, which has different levels of performance for Class 1 and Class 2 instruments.

For example, the Cirrus doseBadge noise dosimeter is marked as meeting IEC 61252:1993 and as such is suitable for use in meeting the Noise at Work regulations ^[1].

If a noise dosimeter has been designed to be used to meet the OSHA standard, or others that require compliance with ANSI standards, additional marking will be required.

The ANSI standard S1.25-1991^[4] required different marking and a noise dosimeter that meets this standard will be marked along the lines of 2AS-90/80-5. This indicates that the unit has tolerances that correspond to a Type 2 sound level meter (ANSI S1.4-1983), with an A Frequency weighting network, an exponetial averager with a Slow time constant, a criterion level of 90dB, a threshold of 80dB and an exchange rate of 5dB.

This is different to the requirements of BS EN 61252:1997 and is not applicable to instruments used to comply with Noise at Work Regulations.

References:

1. Controlling noise at work – The Control of Noise at Work Regulations 2005 – Appendix 1, Section 16

2. BS EN 61252:1997 – Electroacoustics – Specifications for personal sound exposure meters

3.  IEC 61252:1993 + A1:2000 – Electroacoustics – Specifications for personal sound exposure

4. ANSI S1.25 – 1991 – Specification for personal noise dosimeters

The action levels described in the regulations are given as daily (LEP,d) or weekly (LEP,w) exposure values along with peak sound pressure levels, all in dB.

A sound level meter cannot measure LEP,d or LEP,w directly as these are calculated from two other parameters which are recorded during the measurement. These are:

• The equivalent continuous A-weighted sound pressure level in decibels that represents the sound the person is exposed to during the working day
• This is commonly known as the Leq and may be shown as LAeq or LAeq,t
• The duration over which the Leq is measured

With this information, you can calculate the LEP,d using the formula given in the Noise at Work Regulations (Schedule 1 Part 1 paragraph 1).

You should also measure the maximum C-weighted peak sound pressure level:

• This will usually be displayed on your sound level meter as Peak(C) dB or LCPeak
• In accordance with the regulations, this should always be measured with C-weighting

With these two measurements for each different activity to be assessed, you can calculate the LEP,d and where required the LEP,w values.

If you will need to provide PPE or hearing protection, you may also need to record additional values such as the C-weighted Leq (LCeq) or the Leq of the noise in Octave Bands.

This information can be used to assess the effectiveness of hearing protection. The optimus red sound level meters can provide these functions in addition to the LAeq and C-weighted peak values.

What do you need to measure these values?

How you make these measurements will depend upon different factors but in most noise measurements are made with either a Sound Level Meter such as the optimus red or a personal noise dosemeter such as the doseBadge.

Sound level meters

Your sound level meter should:

• At a minimum be capable of measuring
• Equivalent Continuous Sound Pressure Level (LAeq)
• C-Weighted Peak Sound Pressure (LCPeak)
• Optionally be capable of measuring
• C-Weighed Leq for selection of PPE using the HML method
• Octave band Leq values for selection of PPE using the Octave Band method
• Meet at least the requirements of
• Class 2 of BS EN 61672-1:2003 (the current standard for sound level meters or
• Type 2 of BS EN 60804:2001 (the former standard)

You should be able to calibrate your sound level meter using an Acoustic Calibrator which meets the requirements of at least Class 2 of BS EN 60942:2003.

To ensure that your equipment is calibrated correctly, you should not use a sound level meter and acoustic calibrator from different manufacturers unless you have very specific information and instructions as to how these two units will work together. It is possible to create large errors in the calibation level which should be avoided wherever possible.

The optimus red sound level meters will provide all of these functions and are the ultimate tool for noise at work measurements.

Noise Dosemeters or Personal Sound Exposure Meters

A noise dosemeter may be very useful for measuring noise exposures of workers who are mobile, driving vehicles, working in environments where access is difficult or where their working pattern varies significantly and may be difficult to predict.

A noise dosemeter should:

• measure the LAeq and LCPeak values over the measurement
• be calibrated in the same way as a sound level meter before, and ideally after, each measurement
• meet the requirements of BS EN 61252:1997 (Note that noise dosemeters have no class or type number)

The doseBadge is the ideal noise dosemeter for this type of noise measurements.

Acoustic Calibrators

An acoustic calibrator should be used to check the meter each day before and after making any measurements.

An acoustic calibrator will generate a tone at a specified level and frequency for a specified microphone. This is the reason that you should not use an acoustic calibrator and sound level meter from different manufacturers without some very detailed and specific information.

Some sound level meters may have an internal electrical calibration. Be aware that this type of calibration does not check the microphone capsule which is the most commonly damaged part of a noise meter.

Your acoustic calibrator should meet at least Class 2 of BS EN 60942:2003.

We would recommend a CR:514 Class 2 Acoustic Calibrator for use with our Class 2 optimus sound level meters and the CR:515 Class 1 Acoustic Calibrator for use with our Class 1 optimus sound level meters.

The Reader unit supplied with the doseBadge features an acoustic calibator that meets these specifications.