Model 950
Operation and
Application Guide Lines
Initial Setup
Select desired operating voltage 115 Vac
or 230 Vac. See note "N" page four.
Set the POWER ON/OFF Switch to ON.
A continuously lit POWER lamp indicates
power applied. Allow the instrument a
three-minute warm-up period to achieve
thermal equilibrium.
To perform initial adjustment and/or
operational testing, set the remaining
front panel controls as follows:
a) The CORNER FREQUENCY switch
and the MULTIPLIER to the desired
corner frequency.
b) The OFFSET control to approximately
mid-range.
c) The GAIN switch to the desired value.
e) The INPUT switch to ground (GND).
Connect a dc-coupled oscilloscope, of
vertical sensitivity 10mV/CM or better, or
a digital voltmeter (DVM) to the
instrument front panel BNC connector
labeled OUT.
Set the OFFSET control for a zero-volt
reading on the scope.
Subsequent changes of CORNER
FREQUENCY and GAIN control settings
will introduce a small dc output offset,
which should be zeroed for critical
applications.
Leaving all other controls unchanged,
set the Input Switch to (A-B) and apply a
5Vdc signal simultaneously to input
BNCs (A) and (B).
The voltage
measured at the OUT BNC should be 5-
5=OVdc. This completes preliminary
test and adjustment.
Corner Frequency Selection
To select a corner frequency, simply set
the CORNER FREQUENCY switch and
the MULTIPLIER switch for the desired
numerical value.
The Differential Input
The instrument utilizes a differential input
amplifier to reject prevalent forms of
electrical interference, while presenting
desirable input characteristics to the
signal source requiring filtering. The
differential input configuration is ideal for
measuring the difference between two
values rather than the values
themselves. Bridge circuits utilizing
strain gages, thermocouples and a
variety of other types of transducers
generate differential full-scale output
voltages in the order of millivolts that are
often superimposed upon volt-level
reference and noise values.
The importance of CMRR
In actual system environments, each
signal and power return conductor can
generate an interference voltage
proportional to the net conductor
resistance and the electrical current
level. Any such interference voltages
appear as common mode signals to the
amplifier, and are rejected as such.
Circuit model illustrating relationship between filter's differential input
amplifier and external signal and error sources.
0d
B
INPUT SIGNAL AND
NOISE VOLTAGE SOURCES
R
SA
*
A
(+)
R
CM+
R
D
10
20
dB
dB
DIFFERENTIAL
INPUT AMPLIFIER
GAIN = K
+
DIFF
AMP
-
*
V
A
V
CM
V
B
OUT
OUTPUT
AMPLIFER
*
SIGNAL
COMMON
R
SB
R
CM-
(±)
B
*
COUPLED
POWER LINE
NOISE VOLTAGE
Vo = K(VA - VB) + Vcm/CMRR : WHERE
K = 1, 10 AND 10 FOR GAIN SETTINGS
OF 0, 10 AND 20dB RESPECTIVELY.
±Vs
(±)
COM
(+)
+Vs
SEE TEXT FOR REMAINING TERMS.
*
DENOTES FRONT PANEL ACCESS
V
P
AC POWER SUPPLY
SIGNAL
COMMON
5
1784 Chessie Lane, Ottawa, IL 61350 • Tel: 800/252-7074, 815/434-7800 • FAX: 815/434-8176
e-mail: sales@freqdev.com • Web Address: http://www.freqdev.com
FREQUENCYDEVICES [ FREQUENCY DEVICES, INC. ]
