HP | Pro 3381 | Specifications | HP Pro 3381 Specifications

HP Pro 3381 Specifications
Model 3380 Series
Tunable Active Filter
Operating Manual
0.1Hz to 200kHz
48dB/Octave Slope
Butterworth and Bessel Response
Low-Pass, High-Pass, Band-Pass, Band-Reject
Model 3381 - Single Channel
Model 3382 - Dual Channel
Model 3384 - Four Channel
Model 3380 Series
0.1Hz to 200kHz (0.005Hz Optional)
1, 2 or 4 Channels, 48dB/Octave Slope
Low-Pass/High-Pass, Butterworth/Bessel Filter
Operating
Manual
Copyright © 2004 Krohn-Hite Corporation. All rights reserved. Contents of
this publication may not be reproduced in any form without the written
permission of Krohn-Hite Corporation. Printed in USA - 9/2004.
15 Jonathan Drive, Unit 4,
Brockton, MA 02301-5566 - Made in U.S.A.
Tel: (508) 580-1660; Fax: (508) 583-8989
E-Mail: sales@krohnhite.com
Ser vice and War ranty
Krohn-Hite Instruments are designed and manufactured in accordance with sound engineering practices and should give
long trouble-free service under normal operating conditions. If your instrument fails to provide satisfactory service and
you are unable to locate the source of trouble, contact our Service Department at (508) 580-1660, giving all the information available concerning the failure.
DO NOT return the instrument without our written or verbal authorization to do so. After contacting us, we will issue a
Return Authorization Number which should be referenced on the packing slip and purchase order. In most cases, we will
be able to supply you with the information necessary to repair the instrument, avoiding any transportation problems and
costs. When it becomes necessary to return the instrument to the factory, kindly pack it carefully and ship it to us prepaid.
All Krohn-Hite products are warranted against defective materials and workmanship. This warranty applies for a period
of one year from the date of delivery to the Original Purchaser. Any instrument that is found within the one year warranty
period not to meet these standards, will be repaired or replaced. This warranty does not apply to electron tubes, fuses or
batteries. No other warranty is expressed or implied.
Krohn-Hite Corporation reserves the right to make design changes at any time without incurring any obligation to incorporate these changes in instruments previously purchased.
Modifications to this instrument must not be made without the written consent of an authorized employee of Krohn-Hite
Corporation.
Model 3380 Series
Table of Contents
Table of Contents
1.0 GENERAL DESCRIPTION · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 1-1
1.1 INTRODUCTION · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 1-1
1.2 SPECIFICATIONS · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 1-1
1.2.1 Functions (Each Channel) · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 1-1
1.2.2 Number of Channels · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 1-1
1.2.3 Filter Characteristics · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 1-1
1.2.4 General · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 1-2
1.2.5 Options · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 1-2
2.0 OPERATION · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-1
2.1 INTRODUCTION · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-1
2.2 TURN-ON PROCEDURE · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-1
2.3 SELF TEST· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-1
2.4 OPERATION · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-1
2.4.1 Front Panel Controls and Display · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-1
2.4.1.1 Channel Selection (Models 3382 and 3384 only) · · · · · · · · · · · · · · · · · 2-1
2.4.1.2 Setting Cutoff Frequency · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-1
2.4.1.3 Digit Select/Frequency Increment and Decrement · · · · · · · · · · · · · · · · 2-2
2.4.1.4 Setting Input Gain (Pre-Filter) · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-2
2.4.1.5 Setting Output Gain (Post Filter) · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-2
2.4.1.6 Butterworth/Bessel Selection [TYPE] · · · · · · · · · · · · · · · · · · · · · · · 2-2
2.4.1.7 Low-Pass and High-Pass Operation – [MODE] · · · · · · · · · · · · · · · · · · 2-2
2.4.1.8 Variable Band-Pass Operation (Models 3382 and 3384 only) · · · · · · · · · · 2-2
2.4.1.9 Variable Band-Reject Operation (Models 3382 and 3384 only)· · · · · · · · · · 2-3
2.4.1.10 AC/DC Coupling · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-3
2.4.1.11 Differential/Single-Ended Input · · · · · · · · · · · · · · · · · · · · · · · · · · 2-3
2.4.1.12 Storing a Filter Setup [STORE] · · · · · · · · · · · · · · · · · · · · · · · · · 2-3
2.4.1.13 Recalling a Filter Setup [RECLL]· · · · · · · · · · · · · · · · · · · · · · · · · 2-3
2.4.1.14 Clear Entry Key – [CE] · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-3
2.4.1.15 All Channel Mode (Models 3382 and 3384) – [ALL CH] · · · · · · · · · · · · · 2-3
i
Table of Contents
Model 3380 Series
Table of Contents
(Continued)
2.5 REAR PANEL DC LEVEL ADJUSTMENTS · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-3
2.5.1 DC Level Adj (Rear Panel) Out · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-3
2.5.2 DC Level Adj (Rear Panel) HP · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-3
2.6 FILTER CHARACTERISTICS · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-4
2.6.1 Amplitude Response · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-4
2.6.2 Phase Response · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-4
2.6.3 Group Delay · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-4
2.6.4 Transient Response · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 2-5
3.0 INCOMING ACCEPTANCE · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 3-1
3.1 INTRODUCTION · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 3-1
3.2 TEST EQUIPMENT REQUIRED · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 3-1
3.3 CUTOFF FREQUENCY ACCURACY · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 3-1
3.4 STOPBAND ATTENUATION· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 3-1
3.5 PRE-FILTER AND POST-FILTER GAIN ACCURACY · · · · · · · · · · · · · · · · · · · · · 3-2
3.6 NOISE CHECK · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 3-2
3.7 COMMON MODE REJECTION · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 3-2
3.8 DISTORTION AND MAXIMUM SIGNAL CHECKS · · · · · · · · · · · · · · · · · · · · · · · 3-2
3.9 AC/DC COUPLING CHECK · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 3-2
4.0 CALIBRATION · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 4-1
4.1 INTRODUCTION· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 4-1
4.2 REQUIRED TEST EQUIPMENT· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 4-1
4.3 CALIBRATION · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 4-1
4.3.1 DC Level · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 4-1
4.3.2 100kHz Differential Input Adjustment · · · · · · · · · · · · · · · · · · · · · · · · · · · 4-2
4.3.3 Unity Gain · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 4-2
4.3.4 High Band Frequency Calibration · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 4-2
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Model 3380 Series
Table of Contents
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Table of Contents
iv
Model 3380 Series
Model 3380 Series
Section 1 - General Description
SECTION 1
GENERAL DESCRIPTION
1.1
IN TRO DUC TION
The Krohn-Hite Model 3380 Filter Series (3381, 3382 and 3384) are one, two or four channel filters providing a tunable
frequency range from 0.1Hz to 200kHz; and with the 002 option, the range is extended to 0.005Hz. The frequency response characteristic is selectable to either maximally flat (Butterworth) for clean filtering in the frequency domain, or
linear phase (Bessel) to provide superior filtering of pulse or complex signals.
Each channel of the 3380 Series is a selectable low-pass or high-pass, 8-pole filter providing an input gain of up to 50dB
and an output gain of up to 20dB, selectable in 0.1dB steps. The 3380 Series will accept input signals of ±10V peak at
0dB gain and has selectable ac or dc coupling. Memory is available for storing set-ups of the instrument which can be recalled later with a simple command. The following pages are the specifications of the Model 3380 Series Filters.
1.2
1.2.1
SPEC I FI CA TIONS
Func tions (Each Chan nel)
Low-pass filter, high-pass filter; 2 or 4 channel models, one or two channel(s) of band-pass or band-reject via external
connections.
1.2.2
Num ber of Chan nels
Model
Channels
3381
1
3382
2
3384
4
1.2.3 Fil ter Char ac ter is tics
Type: Selectable 8-pole Butterworth or 8-pole Bessel.
Attenuation: 48dB/octave.
Tunable Frequency Range fc: 0.1Hz to 200kHz; (option 002, 0.005Hz).
Frequency Resolution: 3 digits, ³1Hz fc; 0.001Hz, <1Hz fc.
Cutoff Frequency Accuracy: ±3%.
Relative Gain at fc: –3.01dB, Butterworth; –12.59dB, Bessel.
1-1
Section 1 - General Description
Model 3380 Series
Passband Gain: ±0.2dB.
High-Pass Bandwidth (0dB Gain): >2MHz.
Stopband Attenuation: >100dB.
Maximum Input: ±10V peak at 0dB gain, reduced in proportion to gain setting.
Pre-Filter Gain: 0dB, 10dB, 20dB, 30dB, 40dB, 50dB, ±0.2dB.
Post-Filter Gain: 0dB to 20dB selectable in 0.1dB
steps, ±0.2dB.
Wideband Noise (2MHz bandwidth detector): 0dB gain, <400µVrms; Max input gain, <5µVrms RTI;
Max. gain <25µVrms RTI.
Harmonic Distortion (1V output): –60dB (0.1%) to 10kHz; –50dB (0.3%) to 200kHz..
Input: Differential or single-ended.
CMRR: >60dB to 10kHz; >50dB to 100kHz.
Sensitivity: 3mV peak with 70dB total gain for 10V peak output.
Impedance: 1 megohm in parallel with 25pf.
Coupling: ac (0.16Hz) or dc.
Maximum DC Component: ±100V in ac coupled mode.
Output:
Maximum Voltage (open circuit): ±10V peak.
Maximum Current: ±80mA peak.
Impedance: 50 ohms.
DC Offset: Adjustable to zero volts.
1.2.4
Gen eral
Crosstalk Between Channels: –80dB for fsig £200kHz, –70dB for fsig >200kHz with input source £50 ohms.
Memory: 9 stored set-ups (0 - 8).
Self-Test Diagnostics: MPU checks unit upon power-up. Display indicates failure mode.
Displays: 7 segment, green, LED; 0.3" high.
Operating Temperature: 0°C to 50°C.
Isolation to Chassis: ±200Vdc.
Input/Output Connectors: BNC.
Power: 3381, 9 watts; 3382, 16 watts; 3384, 30 watts.
Dimensions and Weights: 3 1 2“ (9cm) high, 14" (35.56cm) wide, 121 2” (31.75cm) deep; 7 lbs (3.18kg) net, 9 lbs (4.09kg)
shipping.
1.2.5
Op tions
002: extends low end cutoff to 0.005Hz.
BK-330: Battery Option, up to 8 hours of operation, rechargable NiCad batteries (factory installation).
1-2
Model 3380 Series
Section 1 - General Description
Rack Mount Kit: Part No. RK-314, permits installation of the Model 3380 Series into a standard 19" rack spacing.
Extended 1 Year Warranty: Part No. EX3380.
Specifications apply at 25°C, ±5°C.
1-3
Section 1 - General Description
Model 3380 Series
This page in ten tion ally left blank.
1-4
Model 3380 Series
Section 2 - Operation
SECTION 2
OPERATION
2.1
IN TRO DUC TION
The Model 3381, 3382 and 3384 Filters are one, two or four channel filters respectively, providing a tunable frequency
range of 0.1Hz to 200kHz (0.005Hz with option 002).
Each channel is selectable low-pass or high-pass, 8-pole with input gain from 0dB to 50dB, selectable in 10dB steps; and
output gain from 0dB to 20dB, selectable in 0.1dB steps.
The input signal can be ±10V peak at 0dB gain and has selectable ac or dc coupling. Memory is available for storing
set-ups of the front panel settings which can be recalled later with a keystroke entry.
Each mode of operation will be explained in this section.
2.2
TURN-ON PRO CE DURE
The Model 3380 line voltage range has been preset for either 115V or 230V, Norm, line voltage. When making any
changes to the line connections, remove the power cord.
To change the Norm/Low line setting, remove the top cover to expose the Norm/Low line switch located near the rear
panel, under the back shield.
To achieve access to the 120V/240V connections, remove the bottom cover and change the connections to the desired
120V
Bottom View
voltage as shown in Figure
240V 2.1.
Figure 2.1 Jumper Settings for 120V/240V Operation
2-1
Section 2 - Operation
Model 3380 Series
Model 3382 Filters
Note: On early models, a 120V/240V switch was provided next to the Norm/Low line switch.
120V
240V
Jumper
120V
240V
Norm
Low
Line Switch
Input
Voltage
Range
(rms)
Norm
108-132
Low
90-110
Norm
216-264
Low
180-220
Install Fuse
Model 3381
Model 3382
Model 3384
.15A
1/4A
1/2A
.1A
1/8A
1/4A
Power Consumption
(watts)
120V/240V
Jumper
120V
240V
Model
3381
Model
3382
Model
3384
8
14
26
9
16
30
8
14
26
9
16
30
Set the 120V/240V and Norm/Low line switch and jumpers as needed according to the table above.
Be sure to change the fuse to the proper rating for the line switch setting selected. Replace the cover.
Plug the line cord into the unit, then the ac outlet.
After reading the Self-Test feature, described next, turn on the Model 3380.
2-2
Model 3380 Series
2.3
Section 2 - Operation
SELF TEST
When the Model 3380 is turned on, the microprocessor performs a self-test routine whereby the entire RAM and ROM
operation is verified. If there is a malfunction, such as a defective RAM or ROM, the word “bad” will appear in the DISPLAY followed by a number 1 or 2. “bad 1” indicates U16, microprocessor is defective and a “bad 2” indicates U17,
EPROM is defective.
When the self-test program has completed, the Model 3380 will return to the setup stored in storage location 0. The
Model 3380 is now ready for operation.
2.4
2.4.1
OP ER A TION
Front Panel Con trols and Dis play
2.4.1.1 Chan nel Se lec tion
(Mod els 3382 and 3384 only)
The up [∆] control key below the CHANNEL display increments the channel number. The various displays and indicators on the front panel (cutoff frequency, gains, etc.) pertain to the channel indicated by this display.
2.4.1.2 Set ting Cut off Fre quency
Data entry keys [0] to [9], [.], [KILO] and [MEGA] set the numeric value of the cutoff frequency desired. To select
1.5kHz, press the [1][.][5] data keys and parameter keys [KILO] and [FREQ]. The cutoff frequency for the channel selected will be indicated in Hertz on the four digit DISPLAY (when [ALL CH] mode is selected, the frequency will be
changed on all channels). The KILO and FREQ keys will be lit.
2.4.1.3 Digit Se lect/Fre quency In cre ment and Dec re ment
When the [SHIFT] key is pressed, followed by the DIGIT SELECT [∆] or [∇] keys, the FREQUENCY DISPLAY will
intensify a digit. Pressing the [SHIFT] followed by the [∆] or [∇] key again, will intensify the next digit or will turn the
DIGIT SELECT off. The [∆] will move the intensified digit to the left and the [∇] will move the intensified digit to the
right (direction is labeled in red to the left of keys).
Pressing the [∆] or [∇] keys will then increment or decrement the intensified frequency digit.
2.4.1.4 Set ting In put Gain
(Pre-Fil ter)
Up [∆] and down [∇] INPUT GAIN SET controls increase or decrease the input amplifier by 10dB. The two digit DISPLAY will indicate either 0dB, 10dB 20dB, 30dB, 40dB or 50dB. May also be set by entering gain desired directly on
the keypad and pressing either the [∆] or [∇] gain key.
2.4.1.5 Set ting Out put Gain
(Post Fil ter)
Up [∆] and down [∇] OUTPUT GAIN SET controls increase or decrease the output amplifier by 0.1dB steps from 0dB
to 20.0dB. For gains <10dB, 0.1dB resolution is displayed. For gains >10dB, only 1dB resolution is displayed; however,
the up [∆] and down [∇] keys continue to increment and decrement the gain by 0.1dB. The full 3-digit resolution may be
seen in the middle display by pressing [SHIFT] the [∆] or [∇] key under the output gain display. Also for gains >10dB,
the decimal point is off for whole dB’s (10, 11, 12, etc.) but on for fractional (10.1 – 10.9, 11.1 – 11.9, etc.). Gain may
also be set by entering gain desired directly on the keypad and pressing either the [∆] or [∇] gain key.
2.4.1.6 Butterworth or Bessel Se lec tion – [TYPE]
When [TYPE] is pressed once, DISPLAY indicates the present filter type, “bu.” (Butterworth) and “bES.” (Bessel).
When pressed again, the type will change (i.e. if the type was “bES.” , the change will be to “bu.”.)
2-3
Section 2 - Operation
Model 3380 Series
2.4.1.7 Low-Pass and High-Pass Op er a tion – [MODE]
When [MODE] is pressed once, DISPLAY indicates the present filter type, “h.P.” (high-pass) and “L.P.” (low-pass).
When pressed again, the type will change (if the type was “L.P.” , the change will be to “h.P.”).
2.4.1.8 Variable Band-Pass Operation
(Models 3382 and 3384 only)
To obtain Band-Pass operation with 48dB per octave attenuation proceed as follows:
Set channel 1 to high-pass mode (this will control the low cutoff frequency). Set channel 2 to low-pass (this will control
the high cutoff frequency). Connect the input signal to channel 1 input, connect the channel 1 output to the channel 2 input and connect the load to the channel 2 output. For the Model 3384, the same can be done with channels 3 and 4 respectively.
The minimum pass-band is obtained by setting the high cutoff frequency equal to the low cutoff frequency. In this condition the insertion loss is nominally 6dB (in the Butterworth mode) and the –3dB cutoff frequencies occur at 0.8 and 1.25
times the mid-band frequency. Insertion loss may be made-up by setting output gains to +6dB.
2.4.1.9 Vari able Band-Re ject Op er a tion
(Models 3382 and 3384 only)
To obtain Band-Reject or Notch operation, proceed as follows:
Connect the two channels in parallel by connecting the input signal to the input of each channel simultaneously. The output from both channels should be added through two equal external resistors in series with each output. The junction of
these resistors becomes the output of the filter. It is recommended that the resistors be approximately 1k ohms and of the
carbon or metal film type if the filter is used at higher frequencies. If the two resistors are not equal, the gain on one side
of the notch will be different than the gain of the other. Insertion loss may be made-up by setting output gains to +6dB.
Set channel 1 for low-pass and channel 2 for high-pass, and adjust the cutoff of each channel for the maximum rejection.
The ideal notch occurs when setting the low cutoff (low-pass) to 0.5 and the high cutoff (high-pass) to 1.5 notch. Insertion loss may be made-up by setting output gains to +6dB.
Caution: Do not exceed specified voltage at terminals.
2.4.1.10 AC/DC Cou pling
Pressing the [SHIFT] key, followed by the [TYPE] key, will display the present input coupling, indicating “AC” or
“dC”. Press [SHIFT] [TYPE] again to toggle between AC and DC.
2.4.1.11 Dif fer en tial/Sin gle-Ended In put
LED indicators are provided on the front panel to indicate which input(s) is (are) active. Pressing [SHIFT] and then the
[+ONLY] key under the Input Gain Display will select single-ended input mode, only the LED beside the +Input of the
selected channel will be lit. Pressing [SHIFT] and then the [DIFF] key, will select the differential input mode and both
LEDs beside the selected channel will be lit.
2.4.1.12 Stor ing a Fil ter Setup – [STORE]
There are 9 storage locations for storing front panel filter setups. The locations are numbered 0 through 8. When
[SHIFT] [RECLL][STORE] is first pressed, the DISPLAY indicates the number of the next memory location available.
For example, the DISPLAY will indicate the following: “n=05”. Pressing [RECLL] again will store the entire filter
set-up into that memory location. If another memory location is desired, enter that location on the keyboard and then
press [SHIFT] [RECLL].When [SHIFT] [RECLL] is preceded by a number (0-8), the 3380 will store the current filter
set-up into the memory location selected.
When [SHIFT] [RECLL] is pressed to indicate the next memory location only, pressing the clear entry key [CE] will restore the DISPLAY to the cutoff frequency setting. The filter settings stored in memory location 0 is automatically recalled at turn-on.
2-4
Model 3380 Series
Section 2 - Operation
2.4.1.13 Re call ing a Fil ter Setup – [RECLL]
When [RECLL] is preceded by a number, it will recall the filter set-up which was stored in the memory location selected.
Selectable locations are 0 to 8.
When first pressed, the DISPLAY indicates the number of the memory location to be recalled. For example, the DISPLAY will indicate the following: “n=05”. Pressing the [RCLL] key again will recall the entire filter set-up from memory location “05”.
When pressed to indicate the memory location to be recalled only, pressing the [CE] (clear entry key) will restore the
DISPLAY to the cutoff frequency setting.
Memory location 0 is automatically recalled at turn-on.
2.4.1.14 Clear En try Key – [CE]
When entering a numeric value in the keyboard, but not specifying a parameter, pressing the clear entry key will restore
the DISPLAY to the current cutoff frequency setting.
When a numeric value and its parameter has been entered and the numeric value is then changed, pressing the [CE] key
will restore DISPLAY to the previous value of that parameter. Pressing the [CE] key continuously will toggle between
the previous keypad entry and the present entry.
When either the [STORE] or [RECALL] key is pressed, the next memory location will be indicated on the DISPLAY.
Pressing the [CE] key will restore DISPLAY to the current cutoff frequency setting.
2.4.1.15 All Chan nel Mode – [ALL CH]
( M o d e l s 3382 and 3384)
When [ALL CH] is pressed, the LED in the [ALL CH] key will light; and when frequency, input/output gain, type, mode,
+only or diff input, and/or coupling is entered or changed, the new setting will be entered in all channels of the filter.
2.5
REAR PANEL DC LEVEL ADJ.
The Model 3380 rear panel has 2, 4 or 8 output dc level adjustments. The following procedure is for adjusting the output
dc level to zero volts for any channel.
2.5.1
DC Level Adj. (Rear Panel) HP
Set the filter to HP at 1.1kHz. Adjust HP for 0V at filter output.
2.5.2
DC Level Adj
(Rear Panel)
Out
At any frequency setting, the output dc level may be adjusted to zero volts for each channel with the rear panel, screwdriver adjust, output dc level control.
2-5
Section 2 - Operation
2.6
Model 3380 Series
FIL TER CHAR AC TER IS TICS
2.6.1 Am pli tude Re sponse
Each channel of the Model 3380 can operate in either the low-pass or high-pass mode at 48dB/octave attenuation and
provide either maximally flat (Butterworth) amplitude response or linear phase (Bessel) operation. Comparative amplitude response characteristics in both modes are shown in Figure 2.2A and 2.2B.
Figure 2.2A Low-Pass Amplitude Response
Figure 2.2B High-Pass Amplitude Response
2.6.2 Phase Re sponse
Phase characteristics of the Model 3380 is shown in Figure 2.3. The graph of the filter response provides output phase
relative to the input over a 10:1 frequency range.
2-6
Model 3380 Series
Section 2 - Operation
Figure 2.3 Phase Response
2.6.3 Group De lay
Group delay1 , shown in Figure 2.4, on opposite page, is defined as the derivative of radian phase with respect to radian
frequency, which is the slope of the phase curve. A flat group delay is considered a linear phase response which corresponds to a constant slope of the phase curve. With linear phase response, the distortion of complex data signals will be
minimized because their various frequency components, due to constant time delay, will not shift relative phase.
In numeric terms, the zero frequency phase slope is –293.7°/Hz for Butterworth and –351.9°/Hz for Bessel, when normalized for a cutoff frequency of 1Hz. This will be 2π times greater in °/Hz for a cutoff of 1 radian/sec or –1845°/Hz and
–2211°/Hz respectively. Dividing by 360 converts °/Hz to radians/radians-per-sec yields a group delay time of 5.13s for
Butterworth and 6.14s for Bessel.
[1] IEEE Standard Dictionary of Electrical and Electronic Terms, Institute of Electrical and Electronic Engineers,
IEEE-STD 100-1977, Second Edition, 1977, page 296. , shown in Figur , shown in Figur
2-7
Section 2 - Operation
Model 3380 Series
2.6.4 Tran sient Re sponse
The normalized response for a unit step voltage applied to the input of the Model 3380 operating in the low-pass mode
with both Butterworth and Bessel response is shown in Figure 2.5, on page 2-12.
Figure 2.4 Group Delay
2-8
Model 3380
Section 3 - Incoming Acceptance
SECTION 3
INCOMING ACCEPTANCE
3.1
IN TRO DUC TION
The following procedure should be used to verify that the Model 3380 filter is operating within specifications. These checks
may be used for incoming acceptance and periodic performance checks. Tests must be made with all covers in place and operating for a minimum of 30 minutes to reach operating temperature. If the unit is not operating within specifications, refer to
Calibration Section of the Maintenance Manual before attempting any detailed maintenance. Before testing, follow the initial
set-up and operating procedure in Section 2.
3.2
TEST EQUIPMENT REQUIRED
The test equipment below is required to perform the following tests:
a.
Low Distortion RC Oscillator: Krohn-Hite Model 4400A or equivalent.
b.
RC Oscillator: 10Hz to 10MHz, frequency response of ±0.025dB from 10Hz to 500kHz. Krohn-Hite Model 4300B or
equivalent.
c.
AC Voltmeter: capable of measuring 100µV to 10Vrms, 10MHz bandwidth, Fluke Model 8920A or equivalent.
d.
Frequency Counter.
e.
Distortion Analyzer: Krohn-Hite Model 6900B or equivalent.
If the [ALL CHAN] key is not lit, press the [ALL CHAN] key to
turn on ALL CHANNEL mode. Perform each test on channel 1,
then repeat it on channel 2.
3.3
CUTOFF FREQUENCY ACCURACY
Place BNC tees on the oscillator’s output and the filter’s `+’ input and set the filter’s input to `+ only’ (press [SHIFT] [∆ input
gain].
3-1
Section 3 - Incoming Acceptance
Model 3380
Connect the frequency counter to the oscillator, the oscillator to the filter `+’ input, and the AC meter to the filter input.
Set the filter to butterworth with the `TYPE’ key, lowpass with the ‘MODE’ key, 0dB input gain, 0dB output gain and
5kHz with the `FREQ’ key . Set the oscillator to 5kHz, 1VRMS. Set the meter to read 0dB (dB and REL mode on the
Fluke 8920). Connect the meter to the filter output; adjust the oscillator frequency to get –3.01dB. The frequency on the
counter should be 5kHz ±3%. Change the filter to highpass, adjust the oscillator frequency for –3.01dB; the counter
should read 5kHz ±3%. Change the filter to lowpass mode, bessel type. Adjust the oscillator frequency for –12.6dB; the
frequency on the counter should be 5kHz ±3%. Change the filter to highpass, adjust the oscillator frequency for
–12.6dB; the counter should read 5kHz ±3%.
Repeat the entire above procedure for 50Hz, 500Hz, 50kHz and 200kHz. It is important to re-reference the voltmeter at
each new frequency since the amplitude of the generator may change with changes in frequency.
3.4
STOPBAND ATTENUATION
Accurate stopband attenuation measurements require some simple precautions because of low level signals. The filter should
be shielded with the top and bottom covers in place. BNC cable only should be used between oscillator, filter and voltmeter,
and no other instruments should be connected.
Set the oscillator to 7Vrms, 20kHz and connect it to the `+’ INPUT with the filter set to a cutoff frequency of 1kHz and 0dB
of Input and Output gain. Connect the OUTPUT through a 6kHz passive high-pass filter, as shown in Figure 3.1, to the
ac voltmeter. (Fluke 8920 should have `low range enable’ pressed in).
Set the filter to low-pass mode. The filter OUTPUT should be <700µVrms (–80dB).
Figure 3.1
3.5
Passive 6kHz High-Pass Filter
PRE-FIL TER AND POST-FIL TER GAIN AC CU RACY
With a BNC tee, connect both the oscillator and the AC meter to the filter `+’ Input. Set the filter to 10kHz, low-pass.
With the meter in volts mode, set the oscillator to 1kHz, and about 700mVrms. Set the meter to read 0dB (dB and REL
mode on the Fluke 8920). Connect the meter to the filter output. Set the input gain to 10dB, the meter should read 9.8 to
10.2dB. Set the input gain to 20dB, the meter should read 19.8 to 20.2dB. Set the input gain to 0dB, set the output gain to
1dB by pressing `1’ and either of the output gain arrows. The meter should read 0.8 to 1.2dB. Set the output gain to 2dB
to 20dB in 1dB steps, checking the meter for ±0.2dB accuracy. Set the output gain to 0dB.
Connect the meter to the filter `+’ Input and set it to volts mode. Set the oscillator to about 70mVrms. Set the meter to
read 0dB (dB and REL mode on the Fluke 8920). Connect the meter to the filter output. Set the input gain to 30dB, the
meter should read 29.8 to 30.2dB. Set the input gain to 40dB, the meter should read 39.8 to 40.2dB.
Connect the meter to the filter input and set it to volts mode. Set the oscillator to about 25mVrms. Set the meter to read
0dB (dB and REL mode on the Fluke 8920). Connect the meter to the filter output. Set the input gain to 50dB, the meter
should read 49.8 to 50.2dB. It is important that the generator be low noise; passive BNC attenuators produce the best results, placed at the filter input.
3-2
Model 3380
Section 3 - Incoming Acceptance
Figure 3.2
3.6
Passive 2MHz Low-Pass Filter
NOISE CHECK
Short the `+’ inputs of both filter channels and set the channel being tested to 0dB input gain, 0dB output gain, lowpass
(mode key), butterworth (type key), DC coupled (press shift then type, if display shows `AC’ press shift type again; display will show `DC’). Connect a 2MHz lowpass, passive filter, shown in Fig 3.2, to the ac voltmeter and, using a short
coax BNC cable, connect it to the model 3380’s output. Set the filter to 5kHz. Voltmeter reading should be 400µV or
less. Set the filter to highpass (mode key). Voltmeter reading should be 400µV or less. Set the filter to 50kHz, lowpass.
Voltmeter reading should be 400µV or less. Set the filter to highpass. Voltmeter reading should be 400µV or less. Set input gain to 50dB and output gain to 20dB (press 20 and either of the output gain arrows). Voltmeter should read 80mV or
less.
3.7
COM MON MODE RE JEC TION
Set the filter to low-pass, 20kHz cutoff and differential input by pressing the shift key, then the DIFF key under the INPUT GAIN display. Set the generator to 10kHz at 7Vrms. Connect the generator to the + and – inputs simultaneously.
Connect the ac voltmeter to the filter output. Reading should be <7mVrms. Set the filter to 200kHz and generator to
100kHz. AC voltmeter should read <25mVrms.
3.8
DIS TOR TION AND MAX I MUM SIG NAL CHECKS
Set the filter to a cutoff frequency of 1kHz in the low-pass mode with 0dB of Input and Output gain. Connect a low distortion oscillator to the INPUT and apply a 1Vrms signal at 1kHz.
CAUTION
If the distortion is excessive, verify that the
distortion of the oscillator being used is <0.005%.
Monitor the OUTPUT of the filter with a distortion analyzer. The reading should be <0.1%.
Connect a 50 ohm terminator to the OUTPUT of the filter. Distortion should be <0.1%. Remove the terminator.
Disconnect oscillator and distortion analyzer.
3-3
Section 3 - Incoming Acceptance
3.9
Model 3380
AC/DC COU PLING CHECK
Apply a 1Vdc signal to the INPUT of the filter. Set the filter to low-pass mode with 0dB Input and Output gain.
In the DC COUPLED mode, the OUTPUT of the filter should be approximately 1Vdc and approximately 0Vdc in the
AC COUPLED mode.
3-4
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