NoiseSensor with 4-20mA Current Loop Output

Installing the MK427 NoiseSensor

The noise sensor would usually be installed at a location close to where the environmental noise is most likely to have an impact. Try to mount away from obstacles and walls that may reflect the noise, and away from any other noise source. The microphone should be at least 1.2m above ground level.

Installation Hardware

The MK427 includes parts to mount it to a pole or similar. These parts include:

• 3 x jubilee clips
• 2 x U-bolts with washers and nuts

The optional CM427 kit can be used to mount the microphone onto a building or other fixed structure.

Detailed Installation Instruction

Detailed installation instructions with details about the electrical and current loop connections are available from our Technical Support web site.

Current Loop Output - 40-20mA

The output from the Noise Sensor is 4-20mA current loop as used by many process control and monitoring systems. The sound level in dB(A) is mapped to the 4-20mA range.

The standard MK427 has a measurement range of 34 to 104 dB(A), but other ranges are available on request. With all ranges the current is proportional to the output:

Iout ∝ 0.1 mA/dB

Connection for current loop, power and actuator (if used) is made using the 10m (32ft) cable that comes pre-installed. A different length cable can be fitted by wiring directly into the unit, as covered in the Installation and User Manual.

DC Voltage Output

The 4-20mA current loop output is generally preferred for control and monitoring systems as the level and accuracy is not degraded by the length of cable (up to a limit). However, if your system needs a DC level then the current can be easily converted.

To convert the 4-20mA output current to a DC voltage output, connect LOOPOUT to the Loop Power Input Ground via a 100Ω resistor for a voltage across the resistor of 10mV/dB.

Types of Calibration

There are different types of calibration, but the three main types that are relevant to this product are:

• Factory Calibration - Carried out by at manufacturer or an approved lab and provides a calibration certificate. The MK427 is provided with a calibration certificate.
• Manual Calibration Check - Carried out on site using a sound level calibrator. Generally once a year or every six months, or if problems are suspected. If you need to do this then you will need the CR515 Sound Level Calibrator.
• Remote Calibration Check - An automatic check that your software can trigger. It uses the built in electrostatic actuator.

Remote Calibration Check

The MK427 NoiseSensor has an electrostatic actuator fitted to the microphone. This is part of the rain-shield, which is hidden inside the windshield.

When it receives a signal the actuator 'excites' the microphone membrane, effectively producing an accurate tone that can be used to check that the microphone sensitivity hasn't drifted. No adjustments are made to the measurement chain, this is designed as a calibration check so your system can detect any significant drift.

To start the actuator an extra connection is needed to the MK427 on top of the normal current loop connections. The actuator needs a voltage of between 5V and 12V applying to this connection.

If you don't need to carry out remote calibration checks then you can simply ignore this facility.

Technical specifications for the MK427 NoiseSensor noise monitor with 4-20mA output.

Output Type	'A' weighted sound level output: 4-20mA loop
Frequency Weighting	dB(A) to IEC 61672 and ANSI S1.4
Time Weighting	Fast (factory option for Slow)
Calibration	Electrostatic actuator with DC voltage control
Measurement Range	34 to 104 dB(A)
	Range options: 24 - 94 dB to 74 - 144 dB (factory fit)
Current Loop Output	Iout = 0.1 mA/dB
Weight	4.5 kg
Mounting	240mm x 30mm diameter pole
	Standard mounting kit: 2 x U-bolts, 3 x jubilee clips
Protection	IP65
Operating Temp.	-10°C to +50°C
Power	9VDC to 36VDC
Output Cable	10m (other lengths are available)