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364
Wiring and Noise Reduction Methods
HP E1415 Noise Rejection
See Figure 6-8 for the following discussion.
Normal Mode Noise
(Enm)
This noise is actually present at the signal source and is a differential noise
(Hi to Lo). It is what is filtered out by the buffered filters on the HP E1502,
E1503, E1508, and E1509 SCPs.
Common Mode
Noise (Ecm)
This noise is common to both the Hi and Lo differential signal inputs. Low
frequency Ecm is very effectively rejected by a good differential
instrumentation amplifier, and it can be averaged out when measured
through the Direct Input SCP (HP E1501). However, high frequency Ecm is
rectified and generates an offset with the amplifier and filter SCPs (such as
HP E1502, HP E1503, HP E1508, and HP E1509). This is since these SCPs
have buffer-amplifiers on board and is a characteristic of amplifiers. The
best way to deal with this is to prevent the noise from getting into the
amplifier.
Keeping Common
Mode Noise out of
the Amplifier
Most common mode noise is about 60 Hz, so the differential amplifier
rejection is very good. The amplifier Common Mode Noise characteristics
are:
120 dB flat to 300 Hz, then 20 dB/octave rolloff
The HP E1415 amplifiers are selected for low gain error, offset, temperature
drift, and low power. These characteristics are generally incompatible with
good high frequency CMR performance. More expensive, high performance
amplifiers can solve this problem, but since they aren’t required for many
systems, HP elected to handle this with the High Frequency Common Mode
Filter option to the HP E1586A Remote Rack Panel (HP E1586 Option 001,
RF Filter) discussed below.
Shielded, twisted pair lead wire generally does a good job of keeping high
frequency common mode noise out of the amplifier, provided the shield is
connected to the HP E1415 chassis ground through a very low impedance.
(Not via the guard terminal - The HP E1415 guard terminal connection
shown in the HP E1415 User’s manual does not consider the high frequency
Ecm problem, and is there to limit the shield current and to allow the DUT
to float up to some DC common mode voltage subject to the maximum
±
16
volt input specification limit.
This conflicts with the often recommended good practice of grounding the
shield at the signal source and only at that point to eliminate line frequency
ground loops, which can be high enough to burn up a shield. We recommend
that you follow this practice, and if you see high frequency common mode
noise (or suspect it), tie the shield to the HP E1415 ground through a 0.1
µ
F
capacitor. At high frequencies, this drives the shield voltage to 0 volts at the
HP E1415 input. Due to inductive coupling to the signal leads, the Ecm
voltage on the signal leads is also driven to zero.
Summary of Contents for VXI 75000 C Series
Page 2: ......
Page 16: ...16 ...
Page 18: ......
Page 30: ...30 Getting Started Chapter 1 Notes ...
Page 32: ...32 Field Wiring Chapter 2 Figure 2 1 Channel Numbers at SCP Positions ...
Page 44: ...44 Field Wiring Chapter 2 Figure 2 11 HP E1415 Terminal Module ...
Page 54: ...54 Field Wiring Chapter 2 Notes ...
Page 61: ...Programming the HP E1415 for PID Control 61 Chapter 3 Programming Overview Diagram ...
Page 136: ...136 Creating and Running Custom Algorithms Chapter 4 Notes ...
Page 152: ...152 Algorithm Language Reference Chapter 5 Notes ...
Page 304: ...304 HP E1415 Command Reference Chapter 6 Command Quick Reference Notes ...
Page 308: ...308 Specifications Appendix A Thermocouple Type E 200 800C SCPs HP E1501 02 03 ...
Page 309: ...Specifications 309 Appendix A Thermocouple Type E 200 800C SCPs HP E1508 09 ...
Page 310: ...310 Specifications Appendix A Thermocouple Type E 0 800C SCPs HP E1501 02 03 ...
Page 311: ...Specifications 311 Appendix A Thermocouple Type E 0 800C SCPs HP E1509 09 ...
Page 312: ...312 Specifications Appendix A Thermocouple Type E Extended SCPs HP E1501 02 03 ...
Page 313: ...Specifications 313 Appendix A Thermocouple Type E Extended SCPs HP E1508 09 ...
Page 314: ...314 Specifications Appendix A Thermocouple Type J SCPs HP E1501 02 03 ...
Page 315: ...Specifications 315 Appendix A Thermocouple Type J SCPs HP E1508 09 ...
Page 316: ...316 Specifications Appendix A Thermocouple Type K SCPs HP E1501 02 03 ...
Page 317: ...Specifications 317 Appendix A Thermocouple Type R SCPs HP E1501 02 03 ...
Page 318: ...318 Specifications Appendix A Thermocouple Type R SCPs HP E1508 09 ...
Page 319: ...Specifications 319 Appendix A Thermocouple Type S SCPs HP E1501 02 03 ...
Page 320: ...320 Specifications Appendix A Thermocouple Type S SCPs HP E1508 09 ...
Page 321: ...Specifications 321 Appendix A Thermocouple Type T SCPs HP E1501 02 03 ...
Page 322: ...322 Specifications Appendix A Thermocouple Type T SCPs HP E1508 09 ...
Page 323: ...Specifications 323 Appendix A 5K Thermistor Reference SCPs HP E1501 02 03 ...
Page 324: ...324 Specifications Appendix A 5K Thermistor Reference SCPs HP E1508 09 ...
Page 325: ...Specifications 325 Appendix A RTD Reference SCPs HP E1501 02 03 ...
Page 326: ...326 Specifications Appendix A RTD SCPs HP E1501 02 03 ...
Page 327: ...Specifications 327 Appendix A RTD SCPs HP E1508 09 ...
Page 328: ...328 Specifications Appendix A 2250 Thermistor SCPs HP E1501 02 03 ...
Page 329: ...Specifications 329 Appendix A 2250 Thermistor SCPs HP E1508 09 ...
Page 330: ...330 Specifications Appendix A 5K Thermistor SCPs HP E1501 02 03 ...
Page 331: ...Specifications 331 Appendix A 5K Thermistor SCPs HP E1508 09 ...
Page 332: ...332 Specifications Appendix A 10K Thermistor SCPs HP E1501 02 03 ...
Page 333: ...Specifications 333 Appendix A 10K Thermistor SCPs HP E1508 09 ...
Page 334: ...334 Specifications Appendix A Notes ...
Page 346: ...346 Glossary Appendix C Notes ...
Page 388: ...388 Generating User Defined Functions Appendix F Notes ...