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Description
Frequency Devices' Model 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 M 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 M'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:
- Adjustable Frequency Control
- Differential Input Amplifiers
- Adjustable Gain Control
- Off-set Adjustment
- BypassControl
- BNC ConnectorsforSignal l/O
An 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
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Models
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900CT |
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Standard AC powered
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900BT |
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AC powered, with battery option
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Available Low-Pass Filters:
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Part#
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#Poles
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Type
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8
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Butterworth |
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8
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Bessel |
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8, 6 zero
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Elliptic, 1.77 |
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8, 6 zero
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Elliptic, 2.00 |
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8, 6 zero
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Constant Delay |
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8, 6 zero
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Constant Delay |
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Available High-Pass Filters:
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Part#
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#Poles
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Type
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8
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Butterworth |
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8, 6 zero
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Elliptic, 1.77 |
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8, 6 zero
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Elliptic, 2.00 |
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Model 900CT
& 900BT
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Tunable Active Filter Instruments
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BLOCK DIAGRAM
| Initial Setup
Select desired operating voltage 115 Vac or 230 Vac. 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.
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.
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Corner Frequency Selection
To select a corner frequency, simply set the three CORNER FREQUENCY switches and the MULTIPLIER switch for the desired numerical value.
The CORNER FREQUENCY switch weightings follow standard decimal positional convention.
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.
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BASE
FREQ
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X
MULT
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RELATIVE
TUNING ACCURACY
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Msd
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Lsd
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B
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C
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D
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E
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| 4 |
0 |
0 |
0.1X
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GREATEST
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| 0 |
4 |
0 |
1X
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LESS
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| 0 |
0 |
4 |
10X
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LEAST
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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.
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Circuit model illustrating relationship between filter's differential input amplifier and external signal and error sources.
Model 900CT
& 900BT
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Location of Front Panel
Terminals and Controls
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| 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.
For 900BT models only: If LED is flashing, recharge batteries, approximately 30 minutes of operation remains.
B. CORNER FREQUENCY Selector Switch (0-400): 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.
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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 either 0, 10, or 20dB.
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.
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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.
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Model 900CT
& 900BT
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Location of Rear Panel Terminals, Controls and Labels
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| 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.
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Q. VOLTAGE Selector Module: The power module window shows the operating voltage (115 Vac or 230 Vac). At time of shipment, the voltage window is set in the 115 Vac position. For 230 Vac operations, use a screwdriver blade to pry open the module door, remove the red fuse cartridge, turn it 180 degrees, reinsert and close the module door. The numerals 230 Vac will now show in the module window. Repeat procedure to change back to 115 Vac.
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Model 900CT
& 900BT
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8-Pole
Low-Pass Filters
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| Model |
900L8B |
900L8L |
900L8E |
900L8EY |
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Filter Specifications
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Transfer Function
Range fc, fr |
8-Pole, Butterworth
0.1 Hz to 49.9 kHz |
8-Pole, Bessel
0.1 Hz to 49.9 kHz |
8-Pole, 6 zero
Elliptic
0.1 Hz to 49.9 kHz
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8-Pole, 6 zero
Elliptic
0.1 Hz to 49.9 kHz |
Theoretical Transfer
Characteristics |
Click to view
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Click to view
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| Tuning Resolution |
1 part in 499
within each decade |
1 part in 499
within each decade |
1 part in 499
within each decade |
1 part in 499
within each decade |
| Passband Ripple |
0.0 dB |
0.0 dB |
±0.035 dB
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-0.05 dB
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Pass Band Voltage
Gain
(non-inverting)
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0 ± 0.1 dB typ.
0 ± 0.2 dB max. |
0 ± 0.1 dB typ.
0 ± 0.2 dB max. |
0 ± 0.1 dB typ.
0 ± 0.2 dB max. |
0 ± 0.1 dB typ.
0 ± 0.2 dB max. |
| Stopband Attenuation |
48 dB/octave |
48 dB/octave |
-80 dB typ.
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-100 dB typ.
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Cutoff Frequency
Accuracy
Stability
Amplitude
Phase |
fc ±2% max.
± 0.5% typ.
± 2% max.
± 0.01% /°C typ.
± 0.02% /°C max.
-3 dB
-360° |
fc ±2% max.
± 0.5% typ.
± 2% max.
± 0.01% /°C typ.
± 0.02% /°C max.
-3 dB
-182° |
fc ±2% max.
± 0.5% typ.
± 2% max.
± 0.01% /°C typ.
± 0.02% /°C max.
-0.035 dB
-323° |
fc ±2% max.
± 0.5% typ.
± 2% max.
± 0.01% /°C typ.
± 0.02% /°C max.
-0.05 dB
-419° |
Filter Attenuation
(theoretical) |
0.12 dB 0.80 fc
3.01 dB 1.00 fc
60.0 dB 2.37 fc
80.0 dB 3.16 fc |
1.91 dB 0.80 fc
3.01 dB 1.00 fc
60.0 dB 4.52 fc
80.0 dB 6.07 fc |
0.35 dB 1.00 fr
3.01 dB 1.13 fr
60.0 dB 1.67 fr
80.0 dB 1.77 fr |
0.05 dB 1.00 fr
3.01 dB 1.06 fr
60.0 dB 1.83 fr
80.0 dB 2.00 fr |
Total Harmonic
Distortion |
< - 90 dB typ. |
< - 90 dB typ. |
< - 90 dB typ. |
<-88 dB typ.
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Wide Band Noise
(5 Hz - 2 MHz) |
200 µVrms typ. |
200 µVrms typ. |
250 µVrms typ. |
250 µVrms typ. |
Narrow Band Noise
(5 Hz - 100 kHz) |
50 µVrms typ. |
50 µVrms typ. |
75 µVrms typ. |
75 µVrms typ. |
Model 900CT
& 900BT
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8-Pole
Low-Pass Filters
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| Model |
900L8D80 |
900L8D10 |
| Product Specifications |
Transfer Function
Range fc |
8-Pole, 6 zero,
Constant Delay
0.1 Hz to 49.9 kHz |
8-Pole, 6 zero,
Constant Delay
0.1 Hz to 49.9 kHz |
Theoretical Transfer
Characteristics |
Click to view
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Click to view
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| Tuning Resolution |
1 part in 499
within each decade |
1 part in 499
within each decade |
| Passband Ripple |
0.15 dB |
0.15 dB |
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Pass Band Voltage
Gain
(non-inverting)
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0 ± 0.1 dB typ.
0 ± 0.2 dB max. |
0 ± 0.1 dB typ.
0 ± 0.2 dB max. |
Stopband
Attenuation |
-80 dB typ. |
-100 dB typ. |
Cutoff Frequency
Accuracy
Stability
Amplitude
Phase |
fc ± 2% max.
± 0.5% typ.
± 2% max.
± 0.01% /°C typ.
± 0.02% /°C max.
-3 dB
-306° |
fc ± 2% max.
± 0.5% typ.
± 2% max.
± 0.01% /°C typ.
± 0.02% /°C max.
-3 dB
-311° |
Filter Attenuation
(theoretical) |
3.01 dB 1.00 fc
60.0 dB 3.08 fc
80.0 dB 3.57 fc |
3.01 dB 1.00 fc
80.0 dB 4.45 fc
100.0 dB 5.20 fc |
Total Harmonic
Distortion @ 1kHz |
< - 90 dB typ. |
< - 88 dB typ. |
Wide Band Noise
(5 Hz - 2 MHz) |
200 µVrms typ. |
200 µVrms typ. |
Narrow Band Noise
(5 Hz - 100 kHz) |
50 µVrms typ. |
50 µVrms typ. |
Model 900CT
& 900BT
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8-Pole
High-Pass Filters
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| Model |
900H8B |
900H8E |
900H8EY |
| Product Specifications |
Transfer Function
Range fc, fr |
8-Pole
Butterworth
0.1 Hz to 49.9 kHz |
8-Pole, 6 zero,
Elliptic
0.1 Hz to 49.9 kHz |
8-Pole, 6 zero,
Elliptic
0.1 Hz to 49.9 kHz |
Theoretical Transfer
Characteristics |
Click to view
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Click to view
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Click to view
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| Tuning Resolution |
1 part in 499
within each decade |
1 part in 499
within each decade |
1 part in 499
within each decade |
| Passband Ripple |
0.0 dB |
± 0.035 dB |
-0.05 dB |
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Pass Band Voltage
Gain
(non-inverting)
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0 ± 0.2 dB to 100 kHz
0 ± 0.5 dB to 120 kHz |
0 ± 0.2 dB to 100 kHz
0 ± 0.5 dB to 120 kHz |
0 ± 0.2 dB to 100 kHz
0 ± 0.5 dB to 120 kHz |
| Power Bandwidth |
120 kHz |
120 kHz |
120 kHz |
Stopband
Attenuation |
48 dB/octave |
-80 dB typ. |
-100 dB typ. |
Cutoff Frequency
Accuracy
Stability
Amplitude
Phase |
fc ± 2% max.
± 0.5% typ.
± 2% max.
± 0.01% /°C typ.
± 0.02% /°C max.
-3 dB
-360° |
fc ± 2% max.
± 0.5% typ.
± 2% max.
± 0.01% /°C typ.
± 0.02% /°C max.
-0.035 dB
-323° |
fc ± 2% max.
± 0.5% typ.
± 2% max.
± 0.01% /°C typ.
± 0.02% /°C max.
-0.05 dB
-419° |
Filter Attenuation
(theoretical) |
80 dB 0.31 fc
60 dB 0.42 fc
3.01 dB 1.00 fc
0.00 dB 2.00 fc |
80 dB 0.56 fr
60.0 dB 0.60 fr
3.01 dB 0.88 fr
0.03 dB 1.00 fr
0.00 dB 2.00 fr |
100 dB 0.50 fr
80.0 dB 0.55 fr
3.01 dB 0.94 fr
0.03 dB 1.00 fr
0.00 dB 2.00 fr |
Total Harmonic
Distortion |
< - 88 dB typ. |
< - 88 dB typ. |
< - 88 dB typ. |
Wide Band Noise
(5 Hz - 2 MHz) |
400 µVrms typ. |
400 µVrms typ. |
500 µVrms typ. |
Narrow Band Noise
(5 Hz - 100 kHz) |
100 µVrms typ. |
100 µVrms typ. |
150 µVrms typ. |
General Specifications
(@ 25°C and rated power Input)
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| Input Characteristics
Input Impedance
- Differential: 2 M shunted by 47pF
- Single Ended: 1 M Shunted by 47pF
Input Voltage
- Linear Differential*: 20V p-p
(Gain Set at 0 dB)
- Max Safe Differential:
Any Continuous Value between ±100V
- Max Safe Common Mode:
Any Continuous Value between ±100V
- Bias Current: 30pA typ.; 175pA max.
- Common Mode Rejection Ratio with 2k Source Unbalance and 0 dB Gain:
> 60dB, DC to 50kHz
Output Characteristics
- Full Power Bandwidth**: dc to 600kHz
- Maximum OutputVoltage:
10V p-p for RL = 50
20V p-p for RL = 2k
- Short Circuit Output Current: ±100 mA continuous
- Output Protection: ±200 mA without damage. (Short Circuit to Ground Only)
- Output Impedance: 50
- Offset Voltage: Adjustable to Zero at Front Panel (Range ±500mV dc)
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Power Supply
(AC Line Power Operation)
- 900CT 10 Watts max.
- 900BT 15 Watts max.
Voltage Frequency Range-Rear Panel:
- 115 V: 105 to 125Vac @ 50/60Hz
- 230 V: 210 to 250Vac @ 50Hz
- Fuse: 115 V=0.2 Amp., 230 V = 2X-0.1 Amp.
Battery Operation (900BT)
- Time for full Charge:
10 to 12 Hrs. @ 20 ºC
- Battery Life:
Approx. 500 Charge-Discharge Cycles
- Battery Charger:
Automatic Uninterruptible
- Charge Status Indicator-Front Panel: 3 Status Levels
- Battery Operation:
6 hours typ.
Temperature
- Operating Temperature:
0 ºC to +50 ºC
- Storage Temperature:
-25 ºC to +70 ºC
Mechanical
- Dimensions:
3.7"H x 8.66"W x 10.6"D,
9.4cmH x 22.0cmW x 27.0cmD
- Weight
900CT 3.5 Ibs; 0.157 kgs.
900BT 4.9 Ibs; 0.219 kgs.
- Case Material: ABS plastic
- Color: Light Gray
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* Signal plus common mode voltage cannot exceed 20V peak for a linear output.
** Output characteristics of input amplifier with filter in BYPASS mode.
Ordering Information
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A. Models
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1. |
900CT
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Standard AC powered model1 |
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2. |
900BT
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AC powered with battery powered option1 |
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FILTER TRANSFER FUNCTIONS AVAILABLE2
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B. LOW-PASS
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BUTTERWORTH |
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1. |
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900L8B |
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8-pole |
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BESSEL |
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2. |
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900L8L |
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8-pole |
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ELLIPTIC |
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3. |
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900L8E |
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8-pole, 6 zero elliptic, 1.77, 80dB |
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4. |
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900L8EY |
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8-pole, 6 zero elliptic, 2.00, 100dB |
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CONSTANT DELAY |
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5. |
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900L8D80 |
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8-pole constant delay, 80dB |
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6. |
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900L8D10 |
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8-pole constant delay, 100dB |
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C. HIGH-PASS
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BUTTERWORTH |
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7. |
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900H8B |
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8-pole |
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ELLIPTIC |
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8. |
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900H8E |
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8-pole, 6 zero elliptic, 1.77, 80dB |
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9. |
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900H8EY |
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8-pole, 6 zero elliptic, 2.00, 100dB |
Note:
- See Item "Q" - Voltage selector Module. At time of shipment, Voltage is pre-selected in the 115 VAC position.
For 230 VAC operation, this this module must be rotated 180 degrees and an additional fuse must be added.
- All filters tunable from 0.1 Hz to 49.9 kHz.
We hope the information given here will be helpful. The information is based on data and our best knowledge, and we consider the information to be true and accurate. Please read all statements, recommendations or suggestions herein in conjunction with our conditions of sale which apply to all goods supplied by us. We assume no responsibility for the use of these statements, recommendations or suggestions, nor do we intend them as a recommendation for any use which would infringe any patent or copyright.
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Certified
