BRUEL & KJAER 2607 User guide

Measuring Amplifier
Type 2607
A portable instrument measuring
true RMS signal levels with
averaging times from
0.1 to 300 sec,
and positive peak, negative peak,
or maximum peak levels with a
rise time
of 20 p, sec. With a B &K
microphone and preamplifier it
conforms to precision sound level
meter recommendations and the
DIN standard for impulse sound
level meters.

MEASURING AMPLIFIER TYPE 2607
November 1970

CONTENTS
1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Front Panel
2.2. Rear Panel
6
................................. 10
3. OPERATION ........................................ 13
3.1. Adjustments ................................ 13
Preliminary Adjustments ...................... 13
Polarization Voltage .......................... 13
Signal or Chassis Ground ....... . .............. 13
3.2. Calibration
for Sound Measurements ............. 14
Using Pistonphone
or Sound Level Calibrator ....... 14
Using Internal Reference Voltage
................ 15
3.3. Measurement
of Sound . . . . . . . . . . . . . . . . . . . . . . . . 16
3.4. Calibration
for Vibration Measurements ........... 17
Using Accelerometer Calibrator 4291 ............. 17 .
Using Internal Reference Voltage . . . . . . . . . . . . . . . . 18
3.5. Measurement
of Vibration ..................... 19
3.6. Calibration
for Voltage Measurements ............ 19
3.7. Voltage Measurements
..... . .................. 20
Input Voltages up to 300 Volts RMS ............. 20
Input Voltages up to 700 Volts Peak ............. 20
3.8. Insert Voltage Calibration
...................... 21
Using Internal Reference Voltage ................ 22
Using
an External Generator . . . . . . . . . . . . . . . . . . . . 22
3.9.
Use of the Averaging Time Socket ............... 23
Remote Selection
of Averaging Time
or Decay Time Constant ....................... 24
Remote Meter Reset . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Remote Indication
of Overload . . . . . . . . . . . . . . . . . 25
Operation of 2607 with Filter Set 1612 ........... 26

4. DESCRIPTION .........................•.•........... 27
4.1.
Input Circuit and Input Amplifier ............... 27
4.2. Reference Oscillator
.......................... 28
4.3.
Input Overload Indicator . . . . . . . . . . . . . . . . . . . . . . 28
4.4. Filter Section
............................... 29
4.5.
Output Section Amplifier ...................... 31
4.6. Output Overload Indicator . . . . . . . . . . . . . . . . . . . . . 33
4.7. RMS Detection and Averaging .................. 33
4.8. Peak Rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.9. Lin/Log Converter ........................... 40
4.1 0. Power Supply ............................... 41
4.11. Overall Characteristics ........................ 41
Dynamic Range ............................. 41
Frequency and Phase Characteristics ............. 44
5. FREQUENCY ANALYSIS AND RECORDING .............. 47
5.1. General .................................... 47
5.2.
RMS Measurements and Statistical Accuracy ....... 47
5.3. Practical Notes
on Recording Analyses ............ 49
Averaging Time with AC Recording .............. 49
Level Recorder Setting for DC output of 2607 ...... 49
Filter Scanning Speed ......................... 50
5.4. Analysis Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
DC Recording ............................... 51
AC Recording . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.5. Power Spectral Density . . . . . . . . . . . . . . . . . . . . . . . . 57
5.6. Tape Recording
............................. 58
6. ACCESSORIES
.......•.....•.•........••.......•..... 61
6.1. General .................................... 61
6.2. Rack Mountings ............................. 61
7. SPECIFICATIONS ......•...........•...............•. 64

1. INTRODUCTION
The 2607 Measuring Amplifier is capable of an extensive range of sound,
vibration and voltage measuremen~s. It combines extreme versatility with a
wide
measurement range and laboratory precision. Used with one of the
8 & K condenser microphones and a suitable preamplifier, the 2607
becomes a precision sound level meter to the I EC Recommendation 179 and
an impulse sound level meter to the German DIN Standard 45633 parts 1
and 2 (March 1967).
It is basically a wide range measuring amplifier for linear as well as
logarithmic operation and includes true RMS and Peak rectifier circuits. The
rectifier circuits contain time constants ranging from 0.1 to 300 sec which
can be directly
or remotely selected to give averaging times for RMS
measurements and decay times for Peak measurements. A display meter
with interchangeable meter scales on which the range setting is automatic-
ally indicated facilitates
the direct calibration of the 2607 for sound
pressure level, acceleration and voltage measurements.
Amongst other features are mains or battery operation, overload indicat-
ors on input and output sections, an internal calibration source and facilities
for the insert voltage calibration of microphones.
The 2607 also contains the internationally standardized sound level
meter frequency weighting networks A, 8 and C as well as the D network
for jet engine noise measurement. For frequency analysis the 2607 may be
used with the 1614/15 Filter Sets or the 2020 Heterodyne Slave Filter. The
analysis may be recorded using the 2305 Level Recorder for which both AC
and DC outputs are available on the 2607. Normally, however, the DC
output will be preferred for recording since a fully averaged RMS signal level
is provided, the accuracy of which is controlled by the time constants of the
2607. This is also an extremely important feature when digital processing of
signal levels is to be performed.
5

2.1. FRONT PANEL
Gain Control
Uncal.
2. CONTROLS
r---Overload Indicators----,
Range Setting Indicator
Meter Function
Averaging
Time
Input Section
Attenuator
Outpu Section
Attenuator
METER SCALE:
Fig.2.1. Front Panel of 2607
Tilt the glass panel forward to slide the scale
out.
Immediately below the meter are two rows of push-buttons. Their funct-
ions are as follows:
POWER:
INPUT:
REF.:
6
On/Off push-button for power.
"Direct" input or input via "Preamplifier"
may be chosen.
Supplies 50 mV, 1 kHz sine wave signal for
internal calibration.

INSERT VOLT. CAL.:
EXT.:
22.4 Hz:
22.4 kHz:
WEIGHTING:
Choice of "Internal" or "External" signal.
"Internal" is 50 mV from the 1 kHz sine wave
generator.
"External" is for connection of a
frequency generator
via rear panel input. The
load impedance is 1 k!1. For use in connect-
ion
with microphone input from the Insert
Voltage Cathode Follower 2617.
Choice of external or internal filter selection.
High
pass filter with cut-off frequency at
22.4 Hz. Sets lower limit of audio frequency
range.
Low pass filter with cut-off frequency at
22.4 kHz. Sets upper limit of audio frequency
range.
For selection
of one of the weighting net-
works D,
A, B or C. When none are selected
the amplifier has a linear frequency response
from 2 Hz to 200 kHz.
The remaining controls and sockets on the
front panel are:
GAIN CONTROL:
UNCAL.:
INPUT SECTI ON
ATTENUATOR:
For continuous control of gain of the input
amplifier. When in position "Cal." the gain is
fixed. Maximum attenuation from "Cal."
position is 10-11 dB. The control operates
with either DIRECT or PREAMP. input
selected.
This light operates when the GAl N
CONTROL knob is in an uncalibrated posit-
ion.
For attenuation
of input signal by 10 dB
steps. Voltages marked around the knob show
the maximum
input voltage (for full scale
deflection) for each knob setting. By using the
7

Gain Control input voltages up to 700 V peak
can be measured. See section 3.7.2.
OVERLOAD INDICATORS: These indicate overload in input or output
amplifiers. While the lights flash the meter
reading
is inaccurate and less than the correct
value.
DIRECT INPUT:
PREAMP. INPUT:
SENS.:
OUTPUT;SECTION
ATTEI"fUATOR:
METER FUNCTION:
LOG/LIN:
8
Coaxial socket input to the input amplifier.
Input impedance 1 MQ//50 pF. Takes B & K
plugs JP 0101.
7 pin socket for connection of B & K micro-
phones via their preamplifiers. Input imped-
ance is 900 kQ//50 pF.
Two screwdriver operated potentiometers
situated
by their respective inputs. They
adjust the gain
of the input amplifier to com-
pensate for different transducer sensitivities.
They
work independently of each other and
each has a range of approx. 14 dB.
Stepped attenuator (10 dB steps) for attenuat-
ion
of the signal level between filter outputs
and the output amplifier. To ensure the best
possible signal/noise ratio the knob should
be
kept as far clockwise as possible.
This selects the appropriate meter character-
istics
for RMS, Impulse and Peak measure-
ments. In the "Impulse Hold" position the
meter
will hold the maximum impulse sound
level value of the applied signal. In the "Peak"
positions, the decay characteristic of the
meter
is as selected on the AVERAGING
TIME control.
Two position switch with the following funct-
ions:
"Log". Meter display and DC output pro-
portional to the measured dB value. Range
50 dB.

AVERAGING TIME:
RESET:
OUTPUT:
AC/DC:
"Lin". Meter display as well as AC and DC
outputs directly proportional to the input
voltage.
For the selection of integrating time constants
to give averaging and decay times ranging
from 0.1
to 300 sec. for RMS and Peak
measurements respectively. Time constants
are also provided for
"Fast" and "Slow"
meter damping characteristics according to
Dl N and I EC standards.
Discharges
the RMS and Peak Rectifier
Circuits of the 2607 to reset the meter for
RMS, Peak and Impulse measurements.
Output socket for AC or DC recording. With
AC the output impedance is 50!1 and the
maximum output is 50 V Peak. The minimum
AC load impedance is 16 k!1//200 pF. With
DC the output impedance is 820!1 and the
output is from 0 to 4.5 V proportional to the
meter deflection. The maximum overrange DC
output for the RMS and Impulse modes is
15 V, and for the Peak mode 25 V.
Selects AC or DC output for recording.
9

2.2. REAR PANEL
Pol.Voltage
Averaging
Time
Socket
Averaging Time
Remote-Manual
Voltage
Selector
AC Power
Socket
Insert Volt.Cal. AC/DC
In Out
Ext. Filter
Selector
Battery
Socket
Fig.2.2. Rear Panel of 2607
POL. VOLT. ADJ.:
POL. VOLTAGE:
AVERAGING TIME
SOCKET:
10
Screwdriver adjustable potentiometer for
microphone polarization voltage.
Socket for measurement of polarization volt-
age with an external DC voltmeter having a
rating
of at least 20 kOJVolt. A ground socket
is situated to the right of this socket.
NOTE: Only signal ground should be used
when checking
the polarization voltage. To
select signal ground see section 3.1.3.
15 pin socket for remote selection of averag-
ing and decay times for RMS and Peak
measurements respectively.
This socket may also be used for the connect-
ion of an overload relay. For connections see
section
3.9.

REMOTE-MANUAL:
VOLTAGE SELECTOR:
AC POWER SOCKET:
INSERT
VOLT. CAL.:
FUSE 5 AMP.:
AC/DC SELECTOR:
Switch
for remote or manual selection of
averaging and decay time constants. When in
the
"Remote" position time constants can be
selected remotely via the AVERAGING TIME
socket. In "Manual" position time constants
selected manually via the AVERAGING TIME
switch.
For selection
of correct mains supply voltage.
To turn the selector, unscrew central AC fuse
with small coin or wide blade screwdriver.
For connection
of AC mains supply with pro-
vision for connecting one of the transformer
shields to the earth of the mains supply. For
connections
see Fig.2.3.
Transformer
shield
AC
Supply
170S09
Fig.2.3. AC POWER socket
Socket for input signal from external generat-
or. Load impedance 1
kil. A ground socket
lies immediately below.
5 Amp fuse for 12 V DC supply.
Switch
to select operation from either mains
or a 12 V
DC supply.
11

BATTERY SOCKET:
EXT. FILTER
INPUT/OUTPUT:
12
3 pin socket
for 12 V DC supply. For
connections see Fig.2.4. The plug required is
JP 4701.
+
!7o~06'
Fig.2.4. BATTERY socket
These sockets are for connection to an
external filter and fit the standard B & K
coaxial plugs. The input impedance of the
External Filter Output is 146 kD,//1 00 pF,
while the output impedance of the External
Filter Input is low (< 1OQ), but must not be
loaded by less than 500n. Max. output volt-
age is 5.6 V peak.

3. OPERATION
3.1. ADJUSTMENTS
3.1.1. Preliminary Adjustments
Before
the instrument is used, the following adjustments should be made:
1. With POWER off and any meter scale fitted, set
the needle deflection
to zero by using the mechanical adjuster under the meter scale.
2. Select
"AC" or "DC" operation with the switch at the rear panel.
If an AC power supply is to be used check the voltage selector so that it
is set to the correct line voltage. If not, remove the central fuse and adjust
with a small coin
or screwdriver.
If DC is used, 12 V ±10% and approx. 2.6 amp. is necessary. It should be
noted
that with DC operation the scale lamps are not lit (saving 2 Watts).
The range indicator lights still operate and show when
the instrument is on.
The above adjustments are part of the normal operating procedure, but
occasionally it may be found necessary to adjust the polarization voltage
and
the signal reference.
3.1.2. Polarization Voltage
The polarization voltage should be measured with a DC voltmeter (meter
rating
20 k!1/V) connected to the POL. VOLTAGE socket. Adjustment is
carried out using the POL. VOLT. ADJ. potentiometer at the rear of the
equipment.
3.1.3. Signal
or Chassis Ground
Choice
of chassis or signal ground is available to suit the requirements of
a particular instrument set-up. Chassis ground is selected by setting the
13

CHASSIS switch to "On" while signal ground is obtained in the "Off"
position. The CHASSIS switch is situated on the main printed circuit board
on the underside
of the apparatus. See Fig.3.1.
Fig.3.1. CHASSISswitch
3.2. CALIBRATION FOR SOUND MEASUREMENTS
3.2.1. Using Pistonphone or Sound level Calibrator
14
1. Carry out the preliminary adjustments, if necessary.
2. Fit the meter scale appropriate to the sensitivity of the microphone
being used. See Table 3.1.
3. Fit the microphone and associated preamplifier.
4. Set controls:
GAIN CONTROL "Cal."
OUTPUT SECTION ATTENUATOR "x 1"
METER FUNCTION "RMS"
AVERAGING TIME "Fast"
REMOTE-MANUAL "Manual"
5. Set the INPUT SECTION ATTENUATOR so that 120 dB (for piston-
phone calibration) or 90 dB (for Sound Level Calibrator calibration) is
indicated as the zero level on the meter scale.

Microphone Open Circuit
8 & K Microphone
Scale No.
Sensitivity Type
26-80 mV per N/m2 4131 4132 SA 0056
4144 4145
2.5- 10 mV per N/m2 4133 4134 SA 0057
0.80- 2.6 mV per Nfm2 4135 4136 SA 0060
0.4 -1.6
mV per N/m2 4138 SA 0083
Table 3.1. Microphone scales for use with 2607
6. Select the appropriate INPUT push button.
Do not select any weighting network.
Switch on and allow
30 sec for the 2607 to warm up.
7. Using a Pistonphone 4220 or Sound Level Calibrator 4230 the meter
should read* 124 or 94 dB respectively. If it does not, adjust the
SENS. potentiometer beside the input socket that is being used, until
the correct deflection is obtained.
3.2.2. Using Internal Reference Voltage
1. Carry out the preliminary adjustments, if necessary.
2. Fit the meter scale appropriate to the sensitivity of the microphone
being used.
See Table 3.1.
3.
Fit the microphone and associated preamplifier.
Any microphone accessories can remain in position.
4. Set controls:
GAIN CONTROL
INPUT SECTION ATTENUATOR
"Cal."
"0.1 V"
OUTPUT SECTION ATTENUATOR "x 1"
METER FUNCTION "RMS"
AVERAGING TIME
REMOTE-MANUAL
"Fast' -'
"Manual"
*For the exact sound pressure, the Pistonphone or Sound Level Calibrator calibration
chart should be consulted.
15

5. Select push buttons:
"Ref."
INPUT as appropriate
Switch on and allow
30 sec. for the 2607 to warm up.
6. From the calibration chart
of the microphone in use, determine its
Open Circuit Sensitivity in mV per N/m2. This must be corrected for
the attenuation and capacitive loading of the preamplifier. For the
Type 2619 Preamplifier
with half inch or one inch microphones, the
total change in sensitivity is less than 0.5 dB. For other types of
preamplifier and other microphones, refer to the instruction manual
for the preamplifier.
7. Using a small screwdriver adjust the SENS. potentiometer
beside the
input socket that is being used, until the required sensitivity is indicat-
ed on the meter scale marked Open Circuit Sensitivity.
3.3. MEASUREMENT OF SOUND
1. Calibrate the meter and microphone as described in section 3.2.
2. Hold the microphone steadily and at least 1 m away from the body
or
set it up on a tripod or other support that will not interfere with the
sound field.
3. Select the weighting network to be used.
4. Keeping the OUTPUT SECTION
ATTENUATOR in the "x 1" posit-
ion
as much as possible, adjust the INPUT SECTION ATTENUATOR
to obtain a suitable meter deflection without overload.
If the INPUT OVERLOAD lamp flashes turn the INPUT SECTION
ATTENUATOR up.
If the OUTPUT OVERLOAD lamp flashes turn the OUTPUT SECT-
ION
ATTENUATOR up.
5. The measured Sound Level
or Sound Pressure Level is the sum of the
meter reading and the attenuator setting displayed by the indicator
lamp on the meter scale.
In reporting sound levels it should always be stated which weighting
network
has been used, e.g. 60 dB (A), 60 dB (D) or for impulse
measurements 60 dB (AI).
The maximum SPLs that can be measured accurately with 1 inch and
1/2 inch microphones with respect to the crest factor of the signal can
be seen in Fig.3.2.
For
further information on sound measurements the booklet "Acoustic
Noise Measurements" is available on request.
16

SPL
160
150
140
130
~
1/<··
It&.
~
~
~, ..
-..............
Mic
~
~
~
2 3 4
t7oMo
Fig.3.2. Max. SPL for 1inch and 1/2 inch microphones
3.4.
CALIBRATION FOR VIBRATION MEASUREMENTS
3.4.1. Using Accelerometer Calibrator 4291
1. Carry out the preliminary adjustments, if necessary.
2. Fit
the meter. scale appropriate to the sensitivity of the accelerometer
being used. See Table 3.2.
3. Fit
the accelerometer and associated preamplifier.
4.
Set knobs:
GAIN CONTROL "Cal."
OUTPUT SECTION ATTENUATOR "x 1"
METER FUNCTION "Max. Peak"
AVERAGING TIME "Fast"
REMOTE-MANUAL "Manual"
.5. Set the INPUT SECTION ATTENUATOR so that a full scale deflect-
ion
of 1 g is indicated on the indicator lights of the meter scale.
6. Select push-button INPUT
"Preamp." or INPUT "Direct" according
to requirement. Switch on and allow 30 sec. for the 2607 to warm up.
Do
not select any weighting networks.
7. Using
the Acceleration Calibrator 4291 vibrate the accelerometer at
1 g peak.
17

Accelerometer
B&K Scale No.
Sensitivity mV/g Accelerometer
Type
1.7-
6 4344 SA 0142
4339 4343
6- 17 SA 0058
4333 4335 4340
17- 60
4332 4334 SA 0143
60-170
4338 SA 0144
Table 3.2. Accelerometer scales for use with 2607
8. With a screwdriver adjust the SENS. potentiometer beside the input
socket that is being used, until a deflection of 1 g Peak is obtained on
the meter scale.
3.4.2. Using Internal Re1 ~ erence Voltage
18
1. Carry
out the preliminary adjustments, if necessary.
2. Fit the meter scale appropriate to the sensitivity of the accelerometer
being used.
3. Fit the accelerometer and appropriate preamplifier.
4. Switch on the instruments and allow 30 sec. for the 2607 to warm up
before proceeding with calibration.
5. From the calibration chart of the accelerometer, calculate what
acceleration level corresponds to a voltage output from the preampli-
fier of 50 mV RMS. For example if a B & K Type 4343 accelerometer
of sensitivity 1 0.1 pC/g is used with a Type 2624 Charge Amplifier on
a gain setting of 1 mV/pC, a voltage level of 50 mV RMS is produced
by a signal of 4.95 g RMS.
6. Set the controls of the Amplifier to:
GAIN CONTROL
"Cal."
OUTPUT SECTION ATTENUATOR "x 1"
METER FUNCTION "RMS"
AVERAGING TIME
REMOTE-MANUAL
INPUT
"Fast"
"Manual"
as appropriate
.·