Type 42AP


Type 42AP
The G.R.A.S. Pistonphone Type 42AP is a battery-operated, precision sound source for accurate and reliable calibration of measurement microphones, sound level meters and other sound measuring equipment.

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 calibration temperature and ambient static pressure.

With a microphone placed in the coupler of the pistonphone, the calibration level and frequency is:

  • nominally 114dB re. 20µPa at either 250Hz or 251.2Hz
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 decibels if measured with an A-weighting filter
  • Static air pressure in hPa
  • Calibration temperature in ºC
  • Calibration temperature in in ºF
The frequency of the pistonphone can be programmed, via its RS-232 interface, to be either 250Hz or 251.2Hz.

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.

The Type 42AP complies with all the requirements of IEC Standard 60942 (2003) LS.

Available accessories:
  • RA0023
    Adapter for 1" microphones
  • RA0024
    Two-port calibration coupler for ½" microphones. Used in comparison calibrations between two ½" microphones; one of which is a reference microphone. It can also be used in measuring the P-I (Pressure-Intensity) Index of intensity probes at 250Hz.
  • RA0072
    Octopus couplers for calibrating up to eight ½" microphones simultaneously. The main coupler of an octopus coupler, which replaces the pistonphone’s normal coupler, is connected to eight separate couplers via narrow-bore flexible tubes 50 cm long. Each of these separate couplers can accept a microphone or a plug substitute.
Specifications Type 42AP
Sound pressure level: 114 dB (re. 20  µPa)  ± 0.09 dB
Frequency: 250 Hz and 251.2 Hz
Temperature range: - 10 °C to + 55 °C
Batteries: 4 × AA alkaline (IEC LR 6)
External power: 6V DC 90 mA
Accuracy: IEC 60942 (ed.3/DIS) LS
Weight: 437 g
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