Description Frequency Devices' Models & 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 1 M shunted 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 to a double-ended single source. Front panel gain control also enables the operator to select a gain factor 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
Standard AC Powered AC Powered, with battery option
Available Low-Pass Filters: Part# #Poles 8, 6 zero 8, 6 zero 8, 6 zero 8, 6 zero Available High-Pass Filters: Part# #Poles 8, 6 zero 8, 6 zero
Filter Type Page Butterworth 6 Bessel 6 Elliptic, 1.77 6 Elliptic, 2.00 6 Constant Delay 7 Constant Delay 7
Block Diagram Front & Rear panel descriptions General Specifications: Ordering Information
1784 Chessie Lane, Ottawa, IL 61350· Tel: 800/252-7074, 815/434-7800· FAX: 815/434-8176 e-mail: email@example.com· Web Address: http://www.freqdev.com
DIFF AMP OFFSET NULLED BYPASS CORNER FREQUENCY TUNING OFFSET TYPICAL ADJUSTMENT FUNCTION
The B, C and D switches combined can select base corner frequency values ranging from 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.
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 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 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.
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.
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.
Vo = K(VA - VB) + Vcm/CMRR : WHERE 1, 10 AND 10 FOR GAIN SETTINGS 0, 10 AND 20dB RESPECTIVELY. +Vs SEE TEXT FOR REMAINING TERMS.