Frequently Asked Questions
We often get asked a range of questions around noise, vibration and air quality. Here are some of the questions we frequently get asked.
We often get asked a range of questions around noise, vibration and air quality. Here are some of the questions we frequently get asked.
You will need to occasionally calibrate your microphone to be confident in its readings. You may already have an acoustic calibrator or pistonphone, or you will have purchased one with your meter. This will need to be professionally calibrated once per year with a certified calibration laboratory. If your acoustic calibrator has a valid certificate, you can calibrate the 97x meters in the Function > Calibration > Calibration by Measurement part of the meter’s menu. For the 958 series, usually Channel 4 is the sound channel. Enter the level of the tone being emitted from the calibrator (usually 94dB or 114dB – check the manual for the instrument) and place the calibrator firmly on the microphone. Take care not to carry this procedure out with high background noise.
If you need a formal instrument calibration carried out, which is recommended every 18-24months, please contact email@example.com with your requirements.
Condenser microphones are extremely stable and sensitive transducers when used in their normal operating conditions. When used for long-term noise monitoring, they can be exposed to more extreme environments (e.g. high temperatures, high windspeeds, moisture, etc) which may cause a change in sensitivity, and even damage. The nature of this type of monitoring often precludes a site visit to calibrate the microphone in the normal way, such as using a sound level calibrator or pistonphone mounted directly on the microphone capsule.
We therefore need a method of checking that all is well at the microphone end, so this describes three methods that can be used.
The SV 307 outdoor noise monitor is fitted with a MEMS microphone, for additional ruggedness and reliability. As such, none of the other two methods can be used. In the case of the SV 307, a small microspeaker is installed in the weather protection, which generates an acoustical signal which can be used for a calibration check.
The SV 307 also includes the possibility of sending alerts if the measured level is outside tolerances, or there is another issue with the patented microphone system.
In this way, you can be sure that measured results are valid.
A more stable and repeatable calibration can be achieved by using an electrostatic actuator mounted on the microphone itself. This takes the form of a plate mounted very close to the microphone diaphragm, and normally replaces the standard protection grid. Some microphones incorporate the actuator in the weather protection system (e.g. rain cover). A variant is to electrically isolate the top plate of the standard microphone grille, so this doubles as the actuator (e.g. the MK255 capsule in the Svantek SV 200).
A signal (typically at 1kHz) is supplied by a generator, via a special amplifier, to create an electrostatic modulation of the microphone diaphragm. This is effectively an acoustic signal, so it checks not only the integrity of the microphone, but also the sensitivity. This is similar to the way microphones are calibrated in the laboratory.
This method therefore requires the generator and amplifier to drive the actuator, and is completely separate to the signal and powering chain of the microphone. Outdoor microphones such as the MTG WME960H have all the necessary electronics integrated, and the actuation can be triggered by a simple contact closure on a serial port for example. This method is used in many long-term monitoring systems, such as the Sinus Swing.
The SV 200 from Svantek is a complete outdoor noise analyser, and has the necessary system built-in. The electrostatic calibration can be triggered via a web page, either manually or automatically at predetermined intervals.
Although this method can be used as a ‘calibration’, the sensitivity of the system is not normally adjusted, but the levels logged to ensure accuracy of the results. Again, because the method requires external electronics and connections, it is not possible to do this via a single co-axial connection such as IEPE.
SysCheck or Charge Injection Calibration which simply injects an electrical signal into the microphone circuit, via the preamplifier, to check the signal path integrity. This includes the microphone capsule itself, which means that any change in the resulting measured signal can be used to deduce if the microphone capacitance has changed, which might be an indicator of damage (e.g. damage or corrosion on the diaphragm, or physical damage).
It’s important to note that this is not a ‘calibration’ as such, it is simply a means to check that nothing has changed out of tolerances, which can be preset by the measuring system. It is not a traceable acoustical signal.
In order to inject the signal, an additional connection is required on the preamplifier, and this is normally available via an industry standard 7-pin Lemo connector, used by many MTG power supplies. This method therefore precludes a simple co-axial connection to the microphone, such as IEPE, which is used solely to provide power to the preamplifier, and return the measured signal. Some front-ends have this calibration method built-in, such as Apollo from Sinus, where the Samurai software can provide the necessary signal on the correct pin of the Lemo connector.
The output of the crystal is a charge, which requires a specialised charge amplifier, with extremely high input impedance, in order to drive our measuring system. These used to be separate boxes, with specialised low-noise cabling, but nowadays, the charge amplifier is built into the accelerometer itself, and this uses a ‘phantom’ powering system known as IEPE (integrated electronic piezo-electric), also known by a variety of proprietary names such as ICP®, CCP etc. At least IEPE is standardised! This means that long cables can be driven, and as long as your instrument can provide the powering, you should be in business. But always check that you have an IEPE accelerometer rather than a charge accelerometer first!
Due to being a capacitor, such accelerometers do not have a DC response, and will roll-off at low frequencies. Make sure you select one suitable for your task, if you want to measure down to 0.5Hz for example.
The majority of accelerometers for our applications are piezoelectric devices. A small piezoceramic crystal is sandwiched between the base and a seismic mass, so when the base is accelerated, the crystal is stressed, causing a proportional charge output. Because it is a simple mass/spring system, it will have a fundamental resonance – the crystal is very stiff, so this will be high, some kilohertz for most devices. Below that resonance, the response is virtually flat and linear, making an excellent transducer.
To make a sensitive accelerometer, make the mass and/or crystal bigger – but, this brings the resonance down, so there’s a trade-off to be made. Thankfully, most requirements for sensitive accelerometers are at low frequencies!
Vibration transducers can be split basically into two types – accelerometers and geophones (or seismometers). Accelerometers have an output proportional to acceleration, and geophones have an output proportional to velocity. So how can both be used to measure vibration?
There’s a basic relationship between acceleration and velocity – the former being the rate of change, or the differential, of velocity. Therefore we can easily convert between the two by integrating an acceleration signal to yield a velocity signal. This is normally done in the time domain, using a filter (called an integrator), but it can also be done in the frequency domain by dividing an acceleration spectrum by 2πf, where f is the frequency. This effectively slopes the spectrum by -6dB/octave, so a velocity spectrum will appear to have a lot fewer high frequency components
Contact force is a measurement of the amount of force between a user’s hand and the tool they’re using. The SV 103 personal vibration dosimeter and the SV 106A (when used with the SV 105AF transducer) are unique in that they measure contact force, which ensures any uncertainty of the measurement to be greatly reduced. You can choose to disregard any data where there is insufficient contact force.
The new dosemeter standard ISO8041-2, under preparation and until recently chaired by Paul Pitts of HSL, will specify a new class of instrument called a Personal Vibration Exposure Meter, which will require contact force measurement. Svantek have the only instruments which currently meets the draft standard, and the SV 103A and SV 106A are the only ones on the market for now.
There are two standards, ISO 8041:2017 and ISO 5349:2001 Parts 1 & 2
ISO 8041 covers the instrument specification, so things like frequency response, weighting filters, detector linearity, measurement parameters etc.
The SV 103 meets the standard.
ISO 5349 is a procedural standard, which tells you what you need (i.e. an instrument which meets ISO 8041), what to measure (e.g. AEQ, triaxial orientation of the hand, etc) and how to do the measurement (practical considerations, what to report, etc).
The SV 103A meets both parts of the standard.
The most common misinterpretation of ISO 5349 is that I have heard people saying you cannot use hand-held accelerometers for the measurement. It does not say this in the standard. It discusses both tool-mounted and hand mounted, and in fact, with many tools (e.g. sanders, polishers, planers etc) it is not possible to use a tool-mounted accelerometer.
Contact firstname.lastname@example.org to request a firmware update and state the model and serial number of the meter. The appropriate firmware and instructions will be sent to you.
To allow for communication between the software you use and the meter, you need to install the appropriate USB drivers for your Windows operating system. You can download the drivers from www.svantek.com Extract the zip file to a location on your hard-drive and install the drivers in the folder corresponding to your Windows operating system. Follow the on-screen instructions. You may need to install the drivers on other USB ports that you wish to use on the same computer.
The answer is simple really – if you want to correctly select hearing protection for your workers.
There are a number of ways to take measurements to help select hearing protection including C-A and HML measurements but these are all compromises compared to taking correct octave band measurements. 1/1 octave analysis is an option for the SV 104A noise dosimeter.
Similar to your noise meter, your vibration meter will need to have a formal calibration carried out every 18-24 months – please contact email@example.com It is also possible to carry out a field calibration with the SV 111 or SV 110 vibration calibrator depending on the type of accelerometer you are using. The latest version of ISO8041 specifies field calibration procedures.
In general, the larger the USB memory, the larger the current requirements, and the slower the speed of the memory. The Svan 95x are low power devices, so have an (intentionally) limited supply of power to the USB host. Therefore, we recommend that the maximum memory size is 4GB, as this provides the best compromise between power, speed and capacity. Larger memory sizes may work perfectly well, but we can’t guarantee it.
Also, we recommend good brands such as Kingston, rather than supermarket own-brand.
If you want to measure noise, have remote communications and measure dominant frequency, then SVAN 958A is the best choice.
No, but 1/1 and 1/3 octave options are available.
Yes, each channel has two profiles, so you can measure unweighted PPV and weighted VDV at the same time.
Yes, the 106A is a six channel instrument so two triaxial locations can be measured.
Yes, with the normal SV84(SV207B) triaxial accelerometer, and 1/3 octaves installed, you can measure VC-A to VC-D, but for measurements to VC-E and NIST-A, we recommend using a 10V/g accelerometer instead, as that gives you more headroom over the noise floor. Typically, three accelerometers are mounted orthogonally in an SA217 block – ask for details.
Yes, if the FFT option is installed, then PPV and dominant frequency can be stored and displayed correctly in SvanPC++ with the threshold criteria.
Yes, if the 958A is equipped with a serial interface and modem (options), then two trigger levels are available on each channel, typically used for warning and alarm levels.
Yes – we use channels 1-3 for vibration, and channel 4 can be used for noise measurements to Class 1 accuracy. Measurements include Leq and Ln as standard, and spectra (if option installed).
Yes, if the WAV option is installed, the ground vibration firmware will also capture the signal file to a USB memory stick.
Yes, if FFT is installed, the ground vibration firmware allows storage of dominant frequency. This is preferred over zero-crossing methods, as it reduces errors caused by complex time waveforms.
In the special ground vibration firmware, 1/3 octave analysis is possible at the same time as PPV and VDV, FFT (option) can also be used.
Yes, in the special ground vibration firmware (included as standard), you can measure both at the same time, although ask yourself why you need to do this – normally VDV is for vibration nuisance/disturbance and PPV is for building damage, so they tend to be measured in different places.
Yes, but you need the 1/3 octave option installed.
Yes, but you need the 1/3 octave option installed.
Yes, you can log individual VDV values with time, e.g. for train pass-bys etc. They can then be accumulated in the SvanPC++ software. Periodic (e.g. hourly) VDV values can be stored at the same time
Yes, it measures VDV according to BS6472, and you can select Wd weighting for the horizontal axes and Wb for the vertical axis. Wg is also available for backwards compatibility with the old version of the standard.
Yes, it measures PPV directly, with selectable high pass filters of 1, 3 and 10Hz. We recommend 3Hz filter for measurements to BS7385
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