Models 900CT & 900BT
Tunable Active
Filter Instrument
Single Channel –
Certified
Description
Frequency Devices’ Models 900CT & 900BT
instruments are single channel; 8-pole low-pass
or high-pass, front panel tunable filter
instruments. The controls allow the user to select
a corner frequency between 0.1 Hz and 49.9 kHz
with a resolution of 1:499 for each of the four
selectable ranges.
The instrument exhibits an input impedance of 1
MΩ shunted by 47pF to a single ended signal
source. When configured in the differential mode,
the instrument has a common mode rejection
ratio (CMRR), which exceeds 60dB; in this mode
the instrument presents an input impedance of 2
MΩ’s shunted by 47pF to a double-ended single
source. Front panel gain control also enables the
operator to select a gain factor of 0, 10, or 20dB.
Standard operational features include:
1) Adjustable Frequency Control
2) Differential Input Amplifiers
3) Adjustable Gain Control
4) Off-set Adjustment
5) Bypass Control
6) BNC Connectors for Signal I/O
The optional battery powered 900BT is
particularly well suited to applications requiring
isolation from an electrically noisy primary power
source.
Compact size and manual rotary switch front
panel controls make 900 instruments a popular,
cost effective, easy-to-use solution for signal
conditioning applications in the following areas:
Anti-aliasing Filters
Biomedical/Biotechnology Applications
Data Recording/Playback
Data Smoothing
EKG/EEG Signal Filtering
FDM/PCM Signal Filtering
Medical Research
Industrial Process Control
Seismic Analysis
Vibration Analysis
Models
900CT
900BT
Standard AC Powered
AC Powered, with battery option
Available Low-Pass Filters:
Part#
#Poles
900L8B
8
900L8L
8
900L8E
8, 6 zero
900L8EY
8, 6 zero
900L8D80
8, 6 zero
900L8D100
8, 6 zero
Available High-Pass Filters:
Part#
#Poles
900H8B
8
900H8E
8, 6 zero
900H8EY
8, 6 zero
Filter Type Page
Butterworth
6
Bessel
6
Elliptic, 1.77
6
Elliptic, 2.00
6
Constant Delay 7
Constant Delay 7
Filter Type
Butterworth
Elliptic, 1.77
Elliptic, 2.00
Page
8
8
8
2
4&5
9
10
Block Diagram
Front & Rear panel descriptions
General Specifications:
Ordering Information
1
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
Models 900CT & 900BT
Model 900 Series
Instrument Block Diagram
BLOCK DIAGRAM
GAIN (dB)
Single Channel –
Certified
INPUT
10dB
0dB
20dB
A-B
A
+
DIFF
AMP
-
OFFSET
NULLED
BYPASS
CORNER
FREQUENCY
TUNING
OFFSET
TYPICAL
ADJUSTMENT
FUNCTION
OUT
A
8-POLE TUNABLE
FILTER
OUTPUT
AMP
B
TYPICAL
FRONT PANEL
BNC CONNECTOR
1
0
2
CORNER FREQUENCY HZ
5
5
3
4
4
6
4
3
2
1
0
9
7
8
3
2
1
6
7 0.1
8
9
MULTIPLIER
10
1
100
0
FRONT PANEL
2
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
Models 900CT & 900BT
Model 900 Series
Initial Setup Procedure
The B, C and D switches combined can
select base corner frequency values
ranging from 1 to 499 Hz in 1 Hz steps
with switch weightings as just described.
The accuracy of the corner frequency is
improved by selecting the largest possible
base frequency and down scaling by the
MULTIPLIER. The greatest accuracy is
obtained with the largest base 400, and
the 0.1X MULTIPLIER switch setting.
Relative accuracy of selected 40 Hz
actual corner frequency for different
multiplier switch settings.
BASE
FREQ
Msd
C
0
4
0
X
MULT
Lsd
E
0.1X
1X
10X
RELATIVE
TUNING ACCURACY
Single Channel –
Initial Setup
Certified
Set the OFFSET control for a zero-volt
reading on the scope or DVM.
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 = 0 Vdc. This
completes
preliminary
test
and
adjustment.
Corner Frequency Selection
To select a corner frequency, simply set
the CORNER FREQUENCY switches and
the MULTIPLIER switch for the desired
numerical value.
Select desired operating voltage 115 V
ac
or 230 V
ac
. See note "Q" on Page 5.
Set the POWER ON/OFF Switch to ON.
A continuously lit POWER lamp indicates
proper internal DC voltages, an essential
requirement for battery-powered models.
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
three
base
CORNER
FREQUENCY
switches
and
the
MULTIPLIER to the desired corner
frequency…
b) The OFFSET control to approximately
mid-range…
c) The GAIN switch to the desired value…
d) The BYPASS switch to OUT…
e) The INPUT switch to ground ( ).
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.
B
4
0
0
D
0
0
4
GREATEST
LESS
LEAST
The CORNER FREQUENCY switch
weightings follow standard decimal
positional conventions.
Circuit model illustrating the relationship between a filter’s differential
input and amplifier and external signal and error sources.
DIFFERENTIAL
INPUT AMPLIFIER
0d
The differential input
The instrument input 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.
INPUT SIGNAL AND
NOISE VOLTAGE SOURCES
R SA
B
10
dB
A
(+)
20
dB
*
GAIN = K
+
DIFF
AMP
-
OUT
V
A
VCM
V
B
R
CM+
R
D
SIGNAL
COMMON
R
SB
R
CM-
(-)
FILTER/
BYPASS
OUTPUT
AMPLIFER
B
-Vs
COM
Vo = K(VA - VB) + Vcm/CMRR : WHERE
K = 1, 10 AND 10 FOR GAIN SETTINGS
OF 0, 10 AND 20dB RESPECTIVELY.
+Vs SEE TEXT FOR REMAINING TERMS.
(+)
COUPLED
POWER LINE
NOISE VOLTAGE
(-)
*
DENOTES FRONT PANEL ACCESS
AC POWER SUPPLY
V
P
OR
INTERNAL BATTERIES
SIGNAL
COMMON
3
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
Models 900CT & 900BT
Model 900 Series
Front Panel Description
D
E
Single Channel –
A
B
Certified
C
Location of Front Panel Terminals and Controls
M
L
K
J
I
H
G
F
A. POWER Status Lamp:
This red LED
indicates whether or not the power to the
analog filter circuitry of a Model 900CT/BT
Series instrument is ON. With the power
switch in the ON position, the LED glows
continuously indicating internal DC power
levels are correct. If LED does not light when
power switch is in ON position, 1) reset
instrument by cycling POWER switch OFF
and ON, 2) Check line fuse.
D. CORNER FREQUENCY
Selector Switch
(0-9): This ten position rotary switch selects
the 1’s digit of the desired corner frequency
between 0 and 9 in discrete increments of 1.
E. MULTIPLIER
Selector Switch: This four-
position rotary switch multiplies by a factor of
either 0.1, 1.0, 10 or 100, the aggregate value
set on the 3 CORNER FREQUENCY selector
switches. (B, C & D)
F. GAIN
Switch: This three-position toggle
switch selects an overall filter gain of 0, 10, or
20 dB.
G. BYPASS
Switch: OUT and IN setting of
this two position toggle switch routes the input
signal to the internal filter or around it,
respectively. E.g. OUT position - no Bypass,
the signal passes through the filter. In either
case, the gain switch remains operational.
H. INPUT
Switch: This three position toggle
configures the instrument for either differential
inputs (A-B), a single-ended input (A), or input
nulling ( ) which grounds both the (A) and (B)
input terminals.
I. & J. (A) and (B)
Input Terminals: This pair
of shielded, female BNC connectors accept
signal inputs (A) and (B). The instrument
applies a non-inverting gain to input (A) and
an equal but opposite inverting gain to input
(B) while the GAIN switch sets the magnitude
of differential gain to 0, 10, or 20 dB. The
BNC shields have been internally connected
to the instrument ground.
K. GROUND
( ) Terminal: This “Banana”
type test jack provides neat and secure
access to the internal ground. This terminal
is a convenient junction for grounding
external
system
and
measurement
instrumentation and/or apparatus.
L. OUT
Terminal: This terminal is a female
BNC connector. The shield on the BNC is
internally connected to the instrument ground.
M. OFFSET
Adjust:
This adjustment is
intended to zero the offset that results from
the instrument’s own circuitry and does not
provide for wide range offset to remove dc
input signals.
For 900BT models only: If LED is flashing,
recharge batteries, approximately 30 minutes
of operation remains.
B. CORNER FREQUENCY
Selector Switch
(0-400Hz): This five position rotary switch
selects the 100’s digit of the corner
frequency designator.
The switch
selectable values are 0, 100, 200, 300 and
400 in five discrete steps.
C. CORNER FREQUENCY
Selector Switch
(0-90):
This ten-position rotary switch
selects the 10’s digit of the desired corner
frequency between 0 and 90, in discrete
increments of 10.
4
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
Models 900CT & 900BT
Model 900 Series
Rear Panel Description
Single Channel –
Certified
Location of Rear Panel Terminals, Controls and Labels
Model
900CT
Feb. 03
SELECT
FUSE
NOM. FREQ.
SN: 00101
115v
(250v 1.0A)
60 Hz
900CT-9L8B
230v
(250v 0.5A)
50 Hz
MADE IN U.S.A.
WARNING:
Do not remove covers, no user serviceable parts inside
.
Contact :
Frequency Devices for service,
tech@freqdev.com
N
O
P
Model
900BT
Feb. 03
SELECT
FUSE
NOM. FREQ.
SN: 00102
115v
(250v 1.0A)
60 Hz
900BT-9L8B
230v
(250v 0.5A)
50 Hz
MADE IN U.S.A.
WARNING:
Do not remove covers, no user serviceable parts inside
.
Contact :
Frequency Devices for service,
tech@freqdev.com
N. IDENTIFICATION LABEL:
This label
identifies the Model number, filter type,
serial number, date of manufacture,
operating
power
limits
and
fuse
requirements of the instrument.
O. AC POWER CONNECTION:
Denotes
plug and fuse location.
P. POWER ON/OFF Switch:
Is a two-
position toggle switch on the back panel
that interrupts/completes the power
circuit.
Q. VOLTAGE Selector Module:
The
power module window shows the
operating voltage (115 V
ac
or 230 V
ac
). At
time of shipment, the voltage window is
set in the 115 V
ac
position. For 230 V
ac
operations, use a screwdriver blade to pry
open the module door, remove the red
fuse cartridge, turn it 180 degrees, re-
insert and close the module door. The
numerals 230 V
ac
will now show in the
module window. Repeat procedure to
change back to 115 V
ac
.
Q
F use
h o ld e r
O p tio n a l
s w itc h
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
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