User's Guide Digital Sound Level Meter Model 407750 Warranty EXTECH INSTRUMENTS CORPORATION warrants this instrument to be free of defects in parts and workmanship for one year from date of shipment (a six month limited warranty applies on sensors and cables). If it should become necessary to return the instrument for service during or beyond the warranty period, contact the Customer Service Department at (781) 890-7440 ext. 210 for authorization or visit our website at www.extech.com (click on ‘Contact Extech’ and go to ‘Service Department’ to request an RA number). A Return Authorization (RA) number must be issued before any product is returned to Extech. The sender is responsible for shipping charges, freight, insurance and proper packaging to prevent damage in transit. This warranty does not apply to defects resulting from action of the user such as misuse, improper wiring, operation outside of specification, improper maintenance or repair, or unauthorized modification. Extech specifically disclaims any implied warranties or merchantability or fitness for a specific purpose and will not be liable for any direct, indirect, incidental or consequential damages. Extech's total liability is limited to repair or replacement of the product. The warranty set forth above is inclusive and no other warranty, whether written or oral, is expressed or implied. Introduction Congratulations on your purchase of the Extech 407750. This device measures sound level in dB and the measurement range can be set automatically or manually. The 407750 offers selectable frequency weighting (‘A’ and ‘C’) and Time Response (Fast and Slow). The built-in RS-232 PC interface allows the user to record readings onto a PC in real-time. Careful use of this meter will provide years of reliable service. Specifications Display Backlit 2000 count LCD with analog bargraph Display update rate Main LCD digits: 0.5 seconds; Bargraph: 50mS Analog Bargraph 1dB steps with 50dB display range Microphone Electret condensor (0.5” diameter) Measurement Bandwidth 31.5Hz to 8KHz Measurement Range A weighting: 30 to 130dB; C weighting: 35 to 130dB 6 ranges in 10 dB steps: 30 to 80dB, 40 to 90dB, 50 to 100dB, 60 to 110dB, 70 to 120dB, 80 to 130dB Accuracy / Resolution ± 1.5dB / 0.1dB Time response selections Fast (125ms) and Slow (1 second) AC and DC Analog outputs 0.707VAC rms at full scale; 10mVDC / dB; 3.5mm output jacks Standards Meets ANSI and IEC Type 2 External Calibrator Extech models 407766 or 407744 Power 9V Battery; 20 hour battery life (typical) with low battery indication Dimensions/weight 3.2 x 10.1 x 1.5” (80 x 256 x 38mm) / 8.5 oz. (240g) 2 Model 407750 Version 2.1 February 2004 Meter Description 1. LCD Display 2. Microphone 3. ON/OFF key 4. REC (Record) key 5. MAXHLD (Max Hold) key 6. C/A Weighting Select key 7. BA (Background Absorber) key 8. F/S Fast / Slow Response select key 9. DOWN 10. Backlit (LCD backlighting) key 11. UPPER 12. AC adaptor jack 13. Calibration screw adjust 14. AC analog output jack 15. DC analog output jack 16. RS-232 output jack Note: The Battery Compartment and the Threaded Tripod mount access are located on the back of the instrument (not pictured) 3 Model 407750 Version 2.1 February 2004 Operation Quick Start 1. Power the meter by pressing the ON/OFF key. 2. The meter’s LCD will count down to zero (99.9, 88.8, 77.7, etc.) and then begin measuring sound levels. If the LCD does not switch on after pressing the ON/KEY check the 9V battery. 3. Point the microphone toward the source of the sound level to be measured and view the reading on the meter’s LCD. ‘A’ and ‘C’ Frequency Weighting Select ‘A’ or ‘C’ weighting via the C/A key. The LCD will reflect the currently selected frequency weighting. Use ‘A’ weighting to have the meter respond as the human ear would with regard to frequency response (the human ear boosts and cuts amplitude over the frequency spectrum). ‘A’ weighting is used for environmental measurements, OSHA regulatory testing, law enforcement, and workplace design. Select ‘C’ weighting for flat responding measurements (less amplitude boost or cut across the frequency spectrum). ‘C’ weighting is used in applications where hearing conservation is not an issue; for example, in the diagnosis of malfunctions in electrical, electronic and mechanical devices. FAST/SLOW Response Time Select either FAST (125ms response) or SLOW (1 second response) measurements by pressing the F/S key. The LCD will reflect the currently selected mode. Selection of ‘Fast’ or ‘Slow’ is determined by the application and any directives or standards related to that application. For example, most hearing conservation or OSHA related testing is done using SLOW and A weighting. MAX HOLD The meter is capable of taking continuous measurements and only updating the LCD when a higher reading (than the one presently on the display) is detected. The bargraph display continues to change while the main LCD waits for a higher reading. Press the MAXHLD key to activate the MAX HOLD mode. The LCD will reflect the MAX HOLD function. Press the MAXHLD key again to return to normal operation. Record (REC) Function To Record the Maximum and Minimum sound level measurements over a programmable period of time, press the REC key. The REC indicator will appear on the LCD. Once the REC key is pressed, the meter begins tracking the highest (MAX) and lowest (MIN) readings. Press the REC again and the MIN indicator will appear on the LCD along with the lowest sound level reading since the REC key was pressed. Press the REC again and the MAX indicator will appear along with the highest reading the meter has encountered since the REC key was first pressed. Press and hold the REC until the REC indicator extinguishes to exit the RECORD mode. 4 Model 407750 Version 2.1 February 2004 BA (Background Noise Absorber) Mode The Background Noise Absorber allows the user to accurately measure equipment noise by “eliminating” background noise. The Sound Level Meter first stores the background noise as a reference level. From there, when a sound is measured, the display will show the sound level measurement minus the background noise. To operate the meter in BA mode, follow these steps: 1. Power the meter. 2. Press the MAXHLD key (the MAX HOLD icon will appear on the LCD). 3. Press the BA key (‘F” will appear to the left of the SPL display icon). 4. Press the MAX HOLD key again (the MAX HOLD icon will reappear on the LCD). 5. The meter is now displaying the background, reference noise. 6. Power the device under test and note the new sound level meter reading. 7. If the reading changes, the new reading is the sound level of the device. If the reading does not change, the noise produced from the device is either equal to or less than the background noise. 8. Press the BA key again to return to the normal mode of operation. Auto and Manual Ranging The meter powers up in the Automatic Range mode. In automatic mode the meter automatically finds the correct range in order to produce the best accuracy. However, if it is desired to set the range manually, follow these steps: 1. Power the meter 2. Notice the two (2) digit number to the immediate left of the analog bargraph. This number is the low end of the presently selected range (see the specifications for the ranges). 3. To change the range, press the UP key to raise the range or press the DOWN key to lower the range. The two digit number on the left of the bargraph will change with each key-press. 4. An advantage of Manual mode is that it takes less time for the meter to take a reading. In Auto Range mode the meter must first locate the correct range before displaying a measurement. LCD Backlighting Press the BACKLIT key to illuminate the LCD. The backlight will remain on for 5 seconds and then automatically switch off to preserve battery life. Auto Power Off To preserve battery life, this meter has an automatic power off feature. If the unit is not used for approximately 20 minutes, the meter shuts off. To override this function, follow these steps: 1. From a power OFF condition, press and hold the ON/OFF and MIN/MAX keys simultaneously. 2. When ‘n’ appears on the display, release the MIN/MAX and then the ON/OFF key. 3. The Auto Power Off feature is now disabled. Note that the Auto Power Off feature is reactivated the next time the meter is powered down. 5 Model 407750 Version 2.1 February 2004 Analog Outputs The meter includes an AC and a DC analog output. These outputs are proportional to the displayed sound level and are ideal for use with chart recorders and dataloggers. The AC output is 0.707V rms full scale and the DC output is 10mV per dB. The labeled 3.5mm output mini-plugs are located on the bottom of the instrument. RS-232 Output The meter includes an RS-232 PC interface jack. This PC interface allows the meter to store and display readings on a PC as they are recorded. The interface cable and software for data acquisition are sold separately. Detailed instructions are provided with the software. 6 Model 407750 Version 2.1 February 2004 Reference Information Frequency Weighting Characteristics Frequency (Hz) 31.5 63 125 250 500 1k 2k 4k 8k A Weighting -39.4dB -26.2dB -16.1dB -8.6dB -3.2dB 0dB +1.2dB +1dB -1.1dB C Weighting -3dB -0.8dB -0.2dB 0dB 0dB 0dB -0.2dB -0.8dB -3dB Tolerance (IEC 651 Type 2) ±3dB ±2dB ±1.5dB ±1.5dB ±1.5dB ±1.5dB ±2dB ±3dB ±5dB Typical A-Weighted Sound Levels dB 140 50HP Siren (100') 130 Jet takeoff (200') 120 110 Riveting machine 100 Subway (20') 90 Pneumatic drill (50') 80 Vacuum cleaner (10') 70 Large store 60 Small office 50 Night residential area 40 Whisper (5'0) 30 20 Chain saw Boiler room Freight train (100') Speech (1') Large Office Residence Sound studio 10 Threshold of hearing 0 7 Model 407750 Version 2.1 February 2004 Battery Replacement When the low battery message appears on the LCD, the 9V battery has fallen to a critically low voltage level and should be replaced as soon as possible. The battery compartment cover resides at the rear of the meter. Remove the rear battery compartment screw and remove the battery compartment cover, change the battery, and replace the compartment cover. Calibration and Repair The meter includes a Calibration adjustment on the bottom of the meter. A sound level calibrator must be used to complete a calibration. Extech can supply a calibrator for this purpose. Once the Calibrator is affixed on the microphone, adjust the calibration screw so that the LCD sound level display matches the calibrator’s output signal. Extech offers repair and calibration services for the products we sell. Extech also provides NIST certification for most products. Call the Customer Service Department for information on calibration services available for this product. Extech recommends that annual calibrations be performed to verify meter performance and accuracy. Support Hotline (781) 890-7440 Tech support: Ext. 200; Email: [email protected] Repair/Returns: Ext. 210; Email: [email protected] Website: www.extech.com Copyright © 2004 Extech Instruments Corporation All rights reserved including the right of reproduction in whole or in part in any form. 8 Model 407750 Version 2.1 February 2004