Background Noise - How does background noise affect measurements?
Background noise can cause considerable error in measurement when the background noise level is close to the level of the noise source of interest. When it is not possible to eliminate or reduce the background noise, a correction factor may be applied to the overall measurement to find the level of the noise of interest. The user must first make a measurement of just the background noise, without the noise source of interest. Then make another measurement with the source of interest. If the difference between the overall measurement and just the background noise is greater than 7dB, then the error due to the background noise is less than 1dB.
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Globe - Should I use the 6-inch or 2-inch globe?
The Globe part of the WBGT measurement calls for a 6-inch (15 cm) diameter hollow copper sphere painted matte black on the outside, or the equivalent. The standard QT-34 and QT-36 sensor bar comes with a 2-inch globe for faster response time. The temperature of the 2-inch globe is correlated to match that of a 6-inch globe. An optional sensor bar with a 6-inch globe is available, if desired, but is not necessary.
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Microphones - Is it okay to swap microphones between dosimeters?
Yes, provided certain actions are taken each time this is done. Microphones are manufactured and tested to performance standards that are applicable to the microphone alone. Likewise the dosimeter electronics are manufactured and tested to performance standards that are applicable to the dosimeter electronics alone. The performance standards of each of these two components of the noise dosimeter are specified tightly enough that any microphone and dosimeter combination that passes their respective independent tests is assured to meet the overall performance standards applicable to the noise dosimeter inclusive of the microphone.
However, variances in sensitivity from one microphone to another must be addressed each time a microphone is swapped from one dosimeter to another. It is considered best practice to perform a field calibration using an acoustical calibrator before each use of a noise dosimeter regardless of whether or not the microphone is swapped. The variances in sensitivity from one microphone to another are automatically resolved when you perform the field calibration.
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NoisePro - What are the factory default settings?
Dosimeter 1 Dosimeter 2 Dosimeter 3
OSHA Hearing
Conservation Controls OSHA Engineering ACGIH
Threshold 80dB 90dB 80dB
Exchange Rate 5dB 5dB 3dB
Criterion Level 90dB 90dB 85dB
Freq. Weighting A A A
Response Time Slow Slow Slow
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Octave Band Filters - What are they and how do I use them?
When a measurement is made with a SLM without the OB filter, the SLM is measuring sound levels over a range of frequencies and combining them into one overall (broad-band) sound level. An OB filter is used to find the sound level just at one specific frequency. When used with an OB filter, the SLM should be set to Fast Response (for quicker settlings after changing frequency selection on the OB filter), and Linear Weighting. The Linear weighting setting will not attenuate, or lessen, the sound level at any frequency.
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QT-34/3 or QT36/3 - Why would I need three sensor bars?
When the temperature in the space surrounding a worker does not have a constant value, it is necessary to determine the WBGT index at three heights corresponding to the worker’s ankles, abdomen, and head. A weighted average is then calculated using those three WBGT measurements. This is based on ISO 7243:1989. Also, one unit may be used to monitor three sensor bars at different locations of a plant, shop, or any area up to 100 feet away.
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QT-34/36 - How are Area Heat Stress Monitors calibrated?
The End user can check the calibration of the area heat stress monitor using the calibration module that is shipped with the monitors. The calibration module is a small connector that plugs into the port on the top of the monitor where the sensor bar is usually assembled. If the QT-34 or QT-36 is out of tolerance, then the monitor must be sent back to Quest for calibration. There is no adjustment for the end user to make.
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SLM - Should the SLM be pointed directly at the sound source or held at an angle?
Quest SLM’s may be used with different types of microphones: free field or pressure. The type of microphone determines the angle at which the SLM should be held. If using a free-field microphone, then the meter’s microphone should be pointed directly at the sound source. If using a pressure type microphone, then the meter should be held at approximately 90 degrees to the sound source. This angle only really matters at higher frequency noises. Refer to the user’s instruction manual for information on the type of microphone used on the meter.
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Type 1 or Type 2 - What is the difference?
This is an accuracy specification. There is an entire ANSI standard written around the difference between Type 1 and 2. The accuracy of the measurements varies depending on the frequency of the sound being measured. Basically Type 1 means approximately ± 1dB accuracy and Type 2 means approximately ± 2dB accuracy. But again, this varies depending upon the frequency of the sound.
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WBGT - What is it?
It stands for Wet Bulb Globe Temperature. It is a weighted averaged of the three sensors on an area heat stress monitor: the Wet Bulb, Globe, and Dry Bulb. The WBGT formula for indoor measurements is 0.7WB + 0.3G. The WBGT formula for outdoor measurements is 0.7WB + 0.2G + 0.1DB.
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