Description Frequency Devices’ Model 950 instruments furnish the user with an 8-pole low-pass or high-pass filter that is tunable by front panel controls. The controls allow the user to select a corner frequency between 10 Hz and 50 kHz with 6 steps from each of two 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 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 BNC ConnectorsforSignal l/O       Compact size and manual rotary switch front panel controls make 950 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   Available Low-Pass Models       950L8B 8-pole Butterworth       950L8L 8-pole Bessel   Available High-Pass Models       950H8B 8-pole Butterworth           Model 950 Tunable Filter Instruments BLOCK DIAGRAM Model 950 Tunable Filter Instruments Model 950L8B 950L8L   Model 950H8B Product Specifications   Low-Pass   High-Pass Transfer Function Range fc 8-Pole, Butterworth 10 Hz to 50.0 kHz 8-Pole, Bessel 10 Hz to 50.0 kHz   Transfer Function Range fc 8-Pole, Butterworth 10 Hz to 50.0 kHz Theoretical Transfer Characteristics Click to view Click to view     Click to view Passband Ripple    (theoretical) 0.0 dB 0.0 dB   Passband Ripple    (theoretical) 0.0 dB DC Voltage Gain    (non-inverting) 0 ± 0.1 dB typ. 0 ± 0.2 dB max. 0 ± 0.1 dB typ. 0 ± 0.2 dB max.   Voltage Gain    (non-inverting) 0 ± 0.2 dB to 100 kHz 0 ± 0.5 dB to 120 kHz         Power Bandwidth 120 kHz Stopband Attenuation Rate 48 dB/octave 48 dB/octave   Stopband Attenuation Rate 48 dB/octave Cutoff Frequency Accuracy Stability Amplitude Phase fc          ± 2% max. ± 0.05% typ. ± 2% max. ± 0.01% /°C typ. ± 0.02%/°C max. -3 dB -360° fc          ± 2% max. ± 0.05% typ. ± 2% max. ± 0.01% /°C typ. ± 0.02%/°C max. -3 dB -182°   Cutoff Frequency Accuracy Stability Amplitude Phase fc          ± 2% max. ± 0.05% typ. ± 2% max. ± 0.01% /°C typ. ± 0.02%/°C max. -3 dB -360° Filter Attenuation 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   Filter Attenuation 80.0 dB        0.31 fc 60.0 dB        0.42 fc 3.01 dB        1.00 fc 0.00 dB        2.00 fc Total Harmonic Distortion @ 1 kHz <-90 dB typ. <-90 dB typ.   Total Harmonic Distortion @ 1 kHz <-88 dB typ. Narrow Band Noise   (5 Hz - 100 kHz) 50 µVrms typ. 50 µVrms typ.   Narrow Band Noise   (5 Hz - 100 kHz) 100 µVrms typ. Model 950 Location of Panel Terminals and Controls Location of Front Panel Terminals and Controls Location of Rear Panel Terminals and Controls FRONT PANEL A. POWER Status Lamp: This red LED indicates whether or not the power to the analog filter circuitry of a Model 950 instrument is on. B. INPUT Switch: This three position toggle configures the instrument for either differential inputs (A-B), a single-ended input (A), or input nulling (GND) which grounds both the (A) and (B) input terminals. C. & D. (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. E. GAIN Switch: This three-position toggle switch selects an overall filter gain of 0, 10, or 20dB.   F. 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. G. CORNER FREQUENCY Selector Switch (10-500Hz): This six position rotary switch selects the digit value of the corner frequency. The switch selectable values are 10, 20, 50, 100, 200 and 500, H. MULTIPLIER Selector Switch: This two-position toggle switch multiplies by a factor of either 1 or 100x, the value set on the CORNER FREQUENCY selector switch. I. OUT Terminal: This terminal is a female BNC connector. The shield on the BNC is internally connected to the instrument ground. REAR PANEL J. IDENTIFICATION LABEL: This label identifies the date of manufacture, serial number, filter type and operating power requirements. K. POWER CONNECTION: Denotes power plug location. L. POWER ON/OFF Switch: A two-position toggle switch on the back panel Power Module that interrupts/completes the power circuit. M. Voltage Selector Module: 115V Operation The power module window shows the operating voltage (115V or 230V). At time of shipment, the voltage window will be set to the 115V position. 230V Operation For 230V operation, use a small flathead screwdriver to pry open the fuse module door. Remove the fuse cartridge, fuse clip and single fuse for 115V operation. Install two 5 X 20 mm 250V, 0.1A fuses into the fuse cartridge, rotate and insert fuse cartridge so 230V is visible in fuse module door when closed. Model 900 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. Specifications (@ 25°C and rated power Input) Input Characteristics Input Impedance Differential: 2 MΩ shunted by 47pF Single Ended: 1 MΩ Shunted by 47pF Input Voltage Linear Differential*: 20V p-p (Gain Set at 0 dB) Max Safe Differential: Any Continuous Value between ±75V Max Safe Common Mode: Any Continuous Value between ±75V Bias Current: 4nA typ.; 20nA max. Common Mode Rejection Ratio with 2kohm Source Unbalance and 0 dB Gain: > 60dB, dc to 50kHz Output Characteristics Full Power Bandwidth: dc to 50kHz Related Output: 10V p-p for RL = 50 Ω, 20V p-p for RL = 2kW Short Circuit Output Current: +/-100 mA continuous Output Protection: +/-200 mA without damage, Short Circuit to Ground Only Output Impedance: 50 W Offset Voltage: Adjustable to Zero at Front Panel (Range +/-500mV dc) Power Supply (AC Line Operation) Power: 6 Watts max. Voltage Frequency Range-Rear Panel: 115 V: 105 to 125Vac @ 50/60Hz 230 V: 210 to 250Vac @ 50Hz Fuse: 0.1 Amp Temperature Operating Temperature: 0 ºC to +50 ºC Storage Temperature: -25 ºC to +70 ºC Mechanical Dimensions: 2.375"H x 7.0"W x 8.3"D 6.03cmH x 17.75cmW x 21.08cmD Weight: 1.5 lbs; 0.68 kgs. Case Material: ABS plastic Color: PC Bone   * Signal plus common mode voltage cannot exceed 20V peak for a linear output.   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.