Servoamplifier and amplifier-detector inspection for gyroscope and accelerometer servo loop

Little, L. J.

English

NASA Technical Reports Server

LMSC/HREC A712335 
LOCKHEED MISSILES & SPACE COMPANY 
HUNTSVILLE RESEARCH & ENGINEERING CENTER 
HUNTSVILLE RESEARCH PARK 
4800 BRADFORD DRIVE, HUNTSVILLE, ALABAMA 
REDUCTION OF ELECTRICAL 
NOJSE AND CROSSTALK 
IN GUIDANCE SYSTEM 
COMPONENTS 
SEPTEMBER PROGRESS REPORT 
15 October 1965 
Contract NAS8 - 201 18 
Prepared for George C. Marshall Space Flight Center 
Huntsville, Alabama 
PREPARED BY: 
L. S. Little 
Systems Engineering 
APPROVED BY: 
R. S. Paulnock 
Mgr., Systems Engineering 
- 
4~ J. S. Far r io r  
Resident Manager 
https://ntrs.nasa.gov/search.jsp?R=19660012486 2020-03-16T22:57:56+00:00Z
I I 
I 
I 
I 
1 
1 
I 
I 
1 
1 
I 
I 
1 
I 
1 
I 
I 
I 
I 
1 
_ _ _ _  
~~ 
LMSC/HREC A712335 
FOREWORD 
This document contains a report of progress for the study contract 
The report was prepared 
"Reduction of Electrical Noise and Crosstalk in Guidance System Components1* 
covering the calendar month of September 1965. 
under Contract NAS8-20118 for the George C. Marshall Space Fiight Center, 
Huntsville , Alabama. 
The effort has, as  its objective, recommendations for reduction of 
crosstalk and improvement of the signal-to-noise ratio in the ST- 124-M 
stabilized platform and its associated electronics. 
NASA/MSFC Technical Supervisors for  the contract a r e  Messrs. 
Owen Rowe and Dave Harper. 
ii 
I 
I 
I 
I 
I 
1 
I 
I 
1 
B 
I 
I 
1 
I 
1 
I 
I 
I 
I 
Cognizant JAS. i 
LMSC/HREC A712335 
WORK ACCOMPLISHED 
.strionics Laboratory personnel were briefed on 
the progress of the servo loop investigation. Four servo loop modules 
e 
0 Ben& servo amplifier, 
e Einersoz~ ser-70 zxnplifier, alrd 
e Power amplifier 
Buff e r amplifie r -detector , 
were inspected for physical and electrical ,ayout characteristics, The 
signal flow and decoupling parameters were given particular attention. 
The discussion section in this report elaborates on the findings 
of the servo electronics investigation. 
I 
I 
LMSC/HREC A712335 
DISCUSSION 
The gyro and accelerometer servo loops a r e  similar in  many respects. 
Essentially, the lead networks, decoupling and amplifier gain a r e  the only 
differences. Therefore, the basic configuration of the two circuits will be 
the same with different component values. in  view of the similarity tf the 
circuits, the analysis of the gyro loop will apply to the accelerometer loop. 
The preamplifier is physically located on the gyro header which 
enables amplifying the e r r o r  signal before it is subjected to the noise 
environment of the platform. 
twisted pair wire to a transformer input of the buffer amplifier. 
and signal common a r e  connected to the dc common which is technically 
sound. 
common very close to the ground plane potential. 
mode rejection of the buffer amplifier should be relatively high. 
The preamplifier's output is wired via a shieided- 
The shield 
This wiring and shielding scheme maintain the shield and the signal 
Therefore, the common 
The buffer amplifier input transformer's Faraday shield would be 
more effective i f  it were connected as illustrated in Figure 1, The purpose 
P r e  amplif ie r 
Buffer 
Amp1 ifie r 
Figure 1 
I 
of the Faraday shield is to reduce the capacitive coupling between the 
transformer's primary and secondary windings. The noise, coupled 
electrostatically, is shunted via the shield to primary capacitance and a 
low impedance connection to the zero potential ground. 
potential ground relative to the signal would be through the shield to the 
s ignal  ground of the preamplifier. Hence, complete electrostatic shielding 
and dc isolation between the two circuits exists. 
The lower 
The Faraday shields in the transformers of the detectors a r e  connected 
appropriately to the signal common in the buffer amplifier-detector module. 
Therefore, dc and electrostatic isolation is present at the input and the output 
of the buffer amplifier-detector -module. 
ing scheme used in the buffer amplifier-detector module. 
Figure 2 shows the signal flow ground- 
2 
LMSC/HREC A712335 
B 
1 
B 
Input Stage 
Base Bias 
Output Signal 
Grounds 
3CR3 
I t -  
OVdc in 
Faraday Shields 
e3 
Figure 2 
Presently, no shielding is used on the servo signal lines in the 
Also, the platform and possibly, no transposition schemes a r e  used. 
shields in cable 603W106 are common which permits crosstalk (see 
Figure 3) by allowing circulating currents in the cable shields. A blanket 
a 
4.8 kc 
Shield 
Figure 3 
shield scheme for the servo signal lines is not practical because of the 
inadequate number of spare pins in connector 52. Therefore, the only 
solution will be to isolate (float) the platform end shields for the servo 
signal lines and ensure that insulated shields a r e  used. 
measure will permit shielding the electrostatic field, the most predominant 
interference, without major modifications. 
The recommended I 
I 
I 
1 
The servo amplifier manufactured by Emerson Electric revealed 
some minor discrepancies i n  signal flow ground paths. 
the physical signal flow routing while Figure 5 presents the intended path 
(reference Emerson print 528860, code number 20418). 
technically correct grounding scheme. Figure 6 contains the Bendix ground 
layout for the servo amplifier. 
layout and presents a minimum interference configuration. Minimum inter - 
ference due to common impedance is present when the higher level circuits 
a r e  closer to the dc power supply. In essence, low level circuits should not 
form a junction with a signal common buss conducting current greater than 
the current flow of the low level circuit. 
Figure 4 illustrates 
Figure 5 is a 
The plan follows the prescribed electrical 
3 
I 
~I 
I 
I 
I 
I 
'I 
I 
1 
I 
I 
I 
I 
I 
I 
I 
I 
.I 
,I 
A2 4 -  
~~ ~~ 
LMSC/HREC A712335 
Signal 
Low 
OVdc 
I I 
Figure 4 
1 1 
A 
Signal 1 1 
Low - I 
Figure 5 
Figure 6 
4 
I 
i 
I 
1 
I 
8 
I 
I 
' I  
i 
I 
I 
i 
I 
I 
1 
I 
1 
I 
LMSG/HREC A712335 
The layout of the power amplifier presented no discrepancies. The 
low level and the high level portions of the signal groundof the circuit a r e  
routed independently to the connector pin that is used for the dc common. 
The decoupling used throughout the servo loop appears compatible 
with the inner stage filtering. 
filter% Bode' plot presents a curve that is down 3 dF3 at approximately 
1 kHz and the decoupling in the buffer has a roll of frequency of approximately 
1 kHz. Similar conditions were found in the servo amplifier and the power 
amplifier. Magnetic shielding should be used on the open frame transformers 
of the servo ioops. 
detector module are in very close proximity and the cores are closely aligned 
which is highly susceptible to cross-coupling of flux leakage. 
For  irrstance, the platform detector output 
Specifically, the h-~ t rzmshrmers  in the bcffer amnlifier- 
r7  
This completes the summary of the problem areas  discovered in 
the servo loops. 
gyros, requires only one investigation to present a composite picture for 
both circuits. 
The similarity between the two loops, accelerometer and 
5 
LMSC/HREC A712335 
PROGRAM PLAN 
A revised summary of the program plan and schedule is shown in 
Table I. Also shown is the predicted manpower assignment throughout 
this contract period and the progress of each of the tasks. All phases of 
the program are on schedule. 
task to be completed. 
The final report  is the only remaining 
FUTURE WORK 
The material collected and analyzed during the tenure of this 
contract is being organized into a final report. 
contract period will be utilized in completing the final report. 
The remainder of the 
6 
. 
~~~ 
LMSC/HREC A712335 
$. 
k 
c, .d
5 
k 
U 
U 
d 
0 
k 
U 
al 
a, 
a, 
.d 
.d 
c, 
A 
P 
il 
A 
6 
ui 1 
7 


Reduction of electrical noise and crosstalk in guidance system components Progress report, Sep. 1965

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server