AC POWER SUPPLY

B

OUTPUT

AMPLIFER

GAIN = K

OUT

COUPLED

POWER LINE

NOISE VOLTAGE

V

B

R

SB

SIGNAL

COMMON

V

P

V

A

V

CM

R

SA

INPUT SIGNAL AND

NOISE VOLTAGE SOURCES

A

(+)

(

±)

R

CM+

+

R

D

R

CM-

-

DIFF

AMP

20dB

10dB

0dB

*

Vo = K(VA - VB) + Vcm/CMRR : WHERE

K = 1, 10 AND 10 FOR GAIN SETTINGS

OF 0, 10 AND 20dB RESPECTIVELY.

SEE TEXT FOR REMAINING TERMS.

DENOTES FRONT PANEL ACCESS

(

±)

(+)

+Vs

COM

±Vs

DIFFERENTIAL

INPUT AMPLIFIER

SIGNAL

COMMON

*

*

*

*

Model 950

Operation and

Application Guide Lines

Circuit model illustrating relationship between filter's differential input

amplifier and external signal and error sources.

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.

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.

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.

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

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