Typical applications and use
- Reference calibration source
- Precision microphone calibrations
- Microphone comparisons
- P-I index measurement at 250 Hz or 251.2 Hz
- Calibration indepenent of atmospheric pressureand altitude
It has a built-in precision barometer and a thermometer. Via its display and RS-232 interface, the user can read the actual corrected sound pressure level, as well as the pistonphone’s temperature and ambient static pressure.
With a microphone placed in the coupler of the pistonphone, the calibration level and frequency is nominally 114 dB* re. 20 μPa at either 250 Hz or251.2 Hz. The actual sound pressure level, corrected for static ambient pressure, is shown on the display of the Pistonphone.
The display can also show the A-weighted sound pressure level after correcting it for using an A-weighting filter.
An individual calibration chart is delivered with each Pistonphone.
The display can be switched to show any of the following:
- Actual corrected sound pressure level in decibels
- Actual corrected sound pressure level in decibelsif measured with an A-weighting filter
- Static air pressure in h Pa
- Calibration temperature in ºC
- Calibration temperature in ºF
The frequency of the pistonphone can be programmed, via its RS-232 interface, to be either 250 Hz or 251.2 Hz.
Remote Control via RS-232 Interface
Commands and responses, comprising ASCII characters, can be sent to and from the Pistonphone via its RS-232 interface, using a suitable utility program.
The interface comprises:
- Connector: RS-232 9-pin D-sub using adapter cable AA0050
- RS-232: 9600,8,n,1 (i.e. 9600 bits per second, 8data bits, no parity bit, 1 stop bit)
There is no flow control/handshaking; therefore commands must be sent one by one, waiting foreach response. The input buffer is 32 bytes; in case of overflow, a response “Buffer overflow” will be submitted. This will not happen under normal conditions.
Commands and Responses
Two types of command are used. These are divided up as follows:
- Interrogational commands
Return information about the Pistonphone, its setup parameters, and measured ambient conditions
- Setup commands
For changing setup parameters and controllingthe Pistonphone.
- Commands are not case sensitive.
- All commands are executed by first typing inthe command then pressing the <Enter> key
The Type 42AP is an extremely stable laboratory standard sound source which can also be used for field calibrations – it retains its high accuracy even under hostile environmental conditions. It complies with all the requirements of IEC Standard 60942(2003) LS.
The 42AP is delivered for calibrating ½" microphones directly since these are most commonly used. A 1" coupler (RA0023) for calibrating 1" microphones is also included.
The pistonphone works on the principle of two reciprocating pistons actuated by a precision-machined cam with a sinusoidal profile. The rotation speed of the cam is controlled to within 0.1% via a tachometer signal in a feed-back loop.
The 42AP has a dual-colour LED above the ON/OFF switch to indicate both battery condition and stable operation.
When the pistonphone is operating properly, the LED shows green, indicating that the speed of the cam is correctly locked to give 250 Hz or, optionally, 251.2 Hz. If it shows red while the pistonphone is switched on, the speed is incorrect; most likely because of low batteries.
The operating procedure is straight forward, simply fit the microphone into the coupler of the pistonphone and switch on. The pistonphone will now produce a constant sound pressure level on the diaphragm of the microphone.
The Pistonphone 42AP is compatible with G.R.A.S. ½", ¼", and ⅛" microphones and all other microphones having the same standard diameters.
Adapters are included for calibrating ¼" and ⅛"microphones. Use the 1" coupler RA0023 for calibrating 1" microphones.
Each pistonphone is factory calibrated with an accuracy of ±0.09dB re. 20μPa and is supplied with an individual calibration certificate stating the exact value and test condition. The exact value is adjusted to be114 dB within ±0.05dB under reference conditions.
Since the output level of a pistonphone depends on the static ambient pressure, the 42AP has a built-in barometer which shows directly on a LCD the actual corrected sound pressure level. Adapters for the G.R.A.S. Environmental Microphone 41AL and Outdoor MicrophoneSystems 41AM and 41CN are available for use with a Pistonphone 42AP fitted with the 1" microphone coupler RA0023.
|Frequency||Hz||250 / 251.2|
|Power supply, external||Vdc||TBD|
|Input signal (max)||Vrms||TBD|
|Microphone polarization output||Vdc||TBD|
|AC output impedance||kΩ||TBD|
|Actuator output impedance||MΩ||TBD|
|Microphone polarization output impedance||MΩ||TBD|
|CE/RoHS compliant/WEEE registered||No/|
|Weight||g / oz||/ TBD|
|G.R.A.S. RA0023||1" microphone coupler|
|G.R.A.S. RA0048||Adapter for ½" microphones. For pistonphone fi tted with the 1" microphone couplerRA0023|
|G.R.A.S. RA0049||Adapter for ¼" microphones|
|G.R.A.S. RA0069||Adapter for ⅛" microphones|
|G.R.A.S. EL0001||Four LR6-AA alkaline cells
|G.R.A.S. RA0009||Adapter for Outdoor Microphone System 41AM. For pistonphone fi tted with the 1" microphone coupler RA0023|
|G.R.A.S. RA0041||Adapter for Outdoor Microphone System 41CN. For pistonphone fi tted with the 1" microphone coupler RA0023|
|G.R.A.S. RA0010||Adapter for Environmental Microphone 41AL. For pistonphone fi tted with the 1" microphone coupler RA0023|
|G.R.A.S. RA0024||Two-port calibration coupler for ½" microphones|
|G.R.A.S. RA0072||Octopus couplers for calibrating up to eight ½" microphones simultaneously|
|G.R.A.S. RA0090||94 dB Pistonphone coupler|