MK:427 Environmental Noise Microphone
Page 12 of 23
Verification & calibration of the MK:427
The standard MK:427 unit is fitted with an electrostatic actuation system that allows the output of
the system to be verified by generating a known sound level.
The system can also be calibrated by using a reference acoustic calibrator and this process is
described on page 14.
Please also refer to the section on page 20, Appendix 3 The influence of the background noise level
on calibration and verification.
Routine verification using the electrostatic actuator system
To carry out a routine verification using the electrostatic actuator system, the MK:427 must have all
of its connections, as specified in the section External Connections.
To activate the electrostatic calibration system, apply any voltage of b5v and +12v level to
the yellow coloured wire. The 0v of this voltage source must be connected to the green coloured
wire.
This voltage needs to be applied during the entire actuation period.
We would recommend waiting for around 20 seconds to ensure the electrostatic actuation system
has time to settle properly before reading the value electrically.
When this voltage level is applied, the actuator 'excites' the microphone to a specific level, which is
shown on the Factory Configuration Information sheet that is supplied with your MK:427.
The output level from the MK:427 will increase to the calibration level which can be used to
calibrate your data logging system.
To end the calibration process, return the voltage on the yellow wire to less than +0.3v.
The electrostatic actuation level will vary between different MK:427 sensors. Refer to page the
Factory Configuration Information sheet for the exact output levels for this instrument.
Explanatory Note – The principle of electrostatic actuation
In an electrostatic actuation system, the level at the microphone membrane level is determined by
the distance between the actuator plate and the microphone capsule membrane, and will vary
between all units.
Once the output calibration current level has been established this should be within ±0.5dB of the
designated level given on the Factory Configuration Information sheet.
If the level has varied to a level that is unacceptable for your application, you should program a
correction into whatever data logging/software system that you are using to receive the analog
signal from the MK:427.
