Keysight 478A Operating And Service Manual
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Keysight 478A Operating And Service Manual

Keysight 478A Operating And Service Manual

Thermistor mount
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Keysight 478A Thermistor
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Operating and
Service Manual

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Summary of Contents for Keysight 478A

  • Page 1 Keysight 478A Thermistor Mount Operating and Service Manual...

  • Page 2: Safety Information

    Conformity. understood and met. where in the EULA. Keysight shall be under no obligation to update, revise or otherwise modify the Software. With WARNING respect to any technical data as defined by FAR 2.101, pursuant to FAR...

  • Page 3: Certification

    This Keysight Technologies instrument product is warranted against defects in material and workmanship for a period of one year from date of shipment. During the warranty period, Keysight Technologies will at its option, either repair or replace products which prove to be defective. For warranty service or repair, this product must be returned to a service facility designated by Keysight Technologies.

  • Page 4: Exclusive Remedies

    Failure to comply with these precautions or with specific warnings elsewhere in this manual violates safety standards for design, manufacture, and intended use of the instrument. Keysight Technologies assumes no liability for the customer’s failure to comply with these requirements.

  • Page 5: Waste Electrical And Electronic Equipment (Weee) Directive

    To return this unwanted instrument, contact your nearest Keysight Service Center, or visit http://about.keysight.com/en/companyinfo/environment/takeback.shtml for more information. Sales and Technical Support To contact Keysight for sales and technical support, refer to the support links on the following Keysight websites: – www.keysight.com/find/478a (product-specific information and support, software and documentation updates) –...
  • Page 6 THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK. Keysight 478A Operating and Service Manual...

  • Page 7: Table Of Contents

    ......... .18 Pulse Energy and Peak Power for 478A/432 Combination .
  • Page 8 ..........50 Keysight 478A Operating and Service Manual...

  • Page 9: List Of Figures

    ........23 Figure 2-5 Schematic Diagram of a Model 478A Thermistor Mount when Connected to a 431 Power Meter .
  • Page 10 ......53 Figure A-9 Keysight Model 478A Printed Circuit Assembly Wiring (P/O Change B) .

  • Page 11: List Of Tables

    List of Tables Table 2-1 Methods of Switching Off RF Output of Various Keysight Signal Generators ......22...
  • Page 12 THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK. Keysight 478A Operating and Service Manual...
  • Page 13 Keysight 478A Thermistor Mount Operating and Service Manual General Information Introduction...

  • Page 14: Figure 1-1 Keysight Model 478A Thermistor Mount

    General Information Figure 1-1 Keysight Model 478A Thermistor Mount Keysight 478A Operating and Service Manual...

  • Page 15: General Information

    To check the thermistor match, proceed as described in “Check on Thermistor Match” page 34. If any damage is found, inform the carrier and your nearest Keysight Sales and Service Office immediately. Keysight 478A Operating and Service Manual...
  • Page 16 General Information THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK. Keysight 478A Operating and Service Manual...
  • Page 17 Keysight 478A Thermistor Mount Operating and Service Manual Operation Biasing Thermistors...

  • Page 18: Operation

    To measure power in excess of 10 mW, insert a calibrated directional coupler such as one of the Keysight Technologies model 770 series or 790 series between the mount and the source. UNDER NO CIRCUMSTANCES APPLY MORE THAN 30 mW AVERAGE POWER TO THE MOUNT.

  • Page 19: Pulse Energy And Peak Power For 478A/432 Combination

    Operation Pulse Energy and Peak Power for 478A/432 Combination For pulses shorter than 250 μs, energy per pulse must not exceed 10 W-μs and peak power should never exceed 200 watts. (For example, a 40 mW, 250 μs pulse contains 10 W-μs of energy.) Pulses longer than 250 μs are allowed to contain more energy but peak power must not exceed 200 W.

  • Page 20: Pulse Energy And Peak Power For 478A/431 Combination

    Operation Pulse Energy and Peak Power for 478A/431 Combination The limitations of this combination are basically the same as the 487A/432 with the exception that at pulse repetition rates less than 1 kHz, energy per pulse must not exceed 5 W-μs and peak power must not exceed 10 mW. These limits are also...

  • Page 21: Figure 2-3 Maximum Power Meter Reading Vs Square And Sine-Wave Frequency

    RF energy contained in the switching pulse itself. This energy must be added to actual RF pulse power when estimating the RF power dissipated in the thermistor mount. PIN diode modulators of Keysight model 8741A/8716A modulators and 8614A/8616A signal generators, however, are not subject to this consideration because output filtering prevents transmission of modulating signals.

  • Page 22: Zero Set

    There is minimum zero drift when the zero is set with the RF system connected to the thermistor mount and the RF power switch off or greatly attenuated by the generator attenuator. The methods used to switch off RF output in Keysight signal generators are listed in Table 2-1.

  • Page 23: Thermistor Mount Disconnected For Zero Set

    When is it inconvenient to turn off the RF power in the RF system, connect the model 478A mount to the RF system and set RANGE on the model 431 power meter for an appropriate midscale reading. When the reading no longer drifts,...
  • Page 24 The presence of this 10-kHz bias signal may affect solid state RF sources and RF voltmeter measurements. To minimize or eliminate these effects, use an additional blocking capacitor at the model 478A or a high pass filter at the RF source output.

  • Page 25: Figure 2-5 Schematic Diagram Of A Model 478A Thermistor Mount When Connected To A 431 Power Meter

    Operation 478A/432 When it is inconvenient to turn the RF power off while using the 478A/432 combination simply remove the mount from the source, and using the COARSE and FINE ZERO, zero the 432. Figure 2-5 Schematic Diagram of a Model 478A Thermistor Mount when...

  • Page 26: Thermoelectric Effect

    An error connection procedure is given in “Thermoelectric Effect Error Correction for 478A / 431 Combination” on page 27. A mild thermocouple exists at each point of contact where the connecting wires to join the thermistor elements.

  • Page 27: Thermoelectric Effect Error Correction For 478A / 431 Combination

    Thermoelectric Effect Error Correction for 478A / 431 Combination Use the following technique to correct for thermoelectric effect error. 1 Measure power 2 Connect an Keysight model 8402 power meter calibration to the power meter DC CALIBRATION AND SUBSTITUTION connector. 3 Zero and null power meter.

  • Page 28: Circuit Description

    The other pair, marked “C” for compensation and situated immediately outside the cavity, is completely shielded from RF. With the 478A attached to 431 power meter, the detection thermistors are part of the metering circuit. With the 478A attached to the 432 power meter, the detection thermistors are part of the RF bridge and the compensation thermistors are part of the compensation bridge.

  • Page 29: 431 Power Meter Detection

    The total power supplied to heat thermistor “C” consists of: – DC bias – Heat from the same environment As “D” and “C” are matched thermally, the total amounts of heat applied to reduce their series resistance equally must be equal. Keysight 478A Operating and Service Manual...
  • Page 30 Operation THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK. Keysight 478A Operating and Service Manual...

  • Page 31: Specifications And Characteristics

    Keysight 478A Thermistor Mount Operating and Service Manual Specifications and Characteristics For the specifications and characteristics of the 478A Thermistor Mount, refer to the datasheet at http://literature.cdn.keysight.com/litweb/pdf/5990-5740EN.pdf...
  • Page 32 Specifications and Characteristics THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK. Keysight 478A Operating and Service Manual...
  • Page 33 Keysight 478A Thermistor Mount Operating and Service Manual Maintenance Mechanical Shock...

  • Page 34: Maintenance

    Maintenance Mechanical Shock The model 478A is a precision instrument. Avoid dropping or other mechanical shocks. Such shocks can destroy the match between the thermistors. Check on Thermistor Match Match between the thermistors may be checked by comparing the thermistor resistances under simulated operating conditions.

  • Page 35: Figure 4-2 Check On Model 478A Thermistor Resistance Match

    Maintenance Under no conditions should the mount be required to carry a current higher WARNING than 14 mA. Figure 4-2 Check on Model 478A Thermistor Resistance Match Keysight 478A Operating and Service Manual...

  • Page 36: Repair

    Maintenance Repair Exceeding the cw or pulse power limit of the model 478A thermistor mount may result in damage such that the mount will no longer zero on the model 431 or 432 power meter. Before adjusting the mount in any way, make sure that the mount is the cause of the problem.

  • Page 37: Figure 4-3 Thermistor Compensation

    Most instruments with serial lower than 7663 do not have the adjusting screws at the time of manufacture, but are modified if the instrument was sent in for repair after March 1964. Keysight 478A Operating and Service Manual...
  • Page 38 5 Replace cover and three screws (A). The instrument is now operative. Make sure the three screws in the body of the thermistor mount are tight when NOTE the mount is put together; this insures quiet operation. Keysight 478A Operating and Service Manual...

  • Page 39: Thermistor Assembly Replacement Procedure

    “Recalibration” on page 43). The procedure consists of removing the damaged thermistor assembly, the printed circuit assembly and replacing them with pretested assemblies included in Thermistor Assembly Replacement Kit, Keysight Stock No. 00478-60002 (see Table 4-1). Table 4-1 Replaceable Parts...
  • Page 40 The following special tools may be required for the completion of this procedure: – One small screwdriver, 0.070 tip, suitable for removing a 00-90 x 1/8 screw. – One pair of tweezers. Keysight 478A Operating and Service Manual...

  • Page 41: Removal Procedure

    RF Thermistors to the Type N center conductor. Remove this screw, if present, using small screwdriver and tweezers. 5 Remove the three 2-56 x 5/8 inch screws holding printed circuit and thermistor assemblies to the RF connector assembly. Keysight 478A Operating and Service Manual...

  • Page 42: Installation Procedure

    Figure 4-5 Keysight Model 478A Printed Circuit Assy Wiring 2 Install the three insulator bushings in the thermistor assembly. 3 Pass the red wire from the thermistor assembly through the hole indicated in Figure 4-5.

  • Page 43: Recalibration

    5 Connect red and white wires from thermistor assembly to printed circuit assembly. 6 Connect thermistor mount to a Keysight model 431. Check for proper null and zero. 7 If desired, check SWR and efficiency. The Mount SWR has been adjusted at the factory to be about equal at 9 GHz and 10 GHz and less than 1.5.
  • Page 44 Maintenance THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK. Keysight 478A Operating and Service Manual...
  • Page 45 Keysight 478A Thermistor Mount Operating and Service Manual Appendix A Introduction Manual Changes...

  • Page 46: Appendix A Introduction

    If your instrument’s serial number is higher than 79401 or not listed in Table A-1, it may be documented in a separate MANUAL CHANGES supplement. Table A-1 Manual Changes by Serial Number Serial Number Make Manual Changes 65600 and below B, A 65601 through 73300 Keysight 478A Operating and Service Manual...

  • Page 47: Manual Changes

    Appendix A Manual Changes Change A Replace Figure 2-5, “Schematic Diagram of a Model 478A Thermistor Mount when Connected to a 431 Power Meter,” on page 25 with Figure A-1. Figure A-1 Schematic Diagram of a Model 478A Thermistor Mount when Connected to a 431 Power Meter.

  • Page 48: Figure A-2 Schematic Diagram Of A Model 478A Thermistor Mount When Connected To A 432 Power Meter

    Appendix A Replace Figure 4-1, “Schematic Diagram of a Model 478A Thermistor Mount when Connected to a 432 Power Meter,” on page 34 with Figure A-2. Figure A-2 Schematic Diagram of a Model 478A Thermistor Mount when Connected to a 432 Power Meter. (P/O Change A)

  • Page 49: Figure A-3 Check On Model 478A Thermistor Resistance Match (P/O Change A)

    Appendix A Replace Figure 4-2, “Check on Model 478A Thermistor Resistance Match,” on page 35 with Figure A-3. Figure A-3 Check on Model 478A Thermistor Resistance Match (P/O Change A) Keysight 478A Operating and Service Manual...

  • Page 50: Change B

    Appendix A Change B Replace Figure 2-4, “Source Impedance Shunting One RF Thermistor Mount,” on page 23 with Figure A-4. Figure A-4 Source Impedance Shunting One RF Thermistor Mount (P/O Change B) Keysight 478A Operating and Service Manual...

  • Page 51: Figure A-5 Schematic Diagram Of A Model 478A Thermistor Mount When Connected To A 431 Power Meter

    Appendix A Replace Figure 2-5, “Schematic Diagram of a Model 478A Thermistor Mount when Connected to a 431 Power Meter,” on page 25 with Figure A-5. Figure A-5 Schematic Diagram of a Model 478A Thermistor Mount when Connected to a 431 Power Meter. (P/O Change B)

  • Page 52: Figure A-6 Schematic Diagram Of A Model 478A Thermistor Mount When Connected To A 432 Power Meter

    Appendix A Replace Figure 4-1, “Schematic Diagram of a Model 478A Thermistor Mount when Connected to a 432 Power Meter,” on page 34 with Figure A-6. Figure A-6 Schematic Diagram of a Model 478A Thermistor Mount when Connected to a 432 Power Meter. (P/O Change B)

  • Page 53: Figure A-7 Thermistor Compensation (P/O Change B)

    4-3, “Thermistor Compensation,” on page 37 with Figure A-7. Figure A-7 Thermistor Compensation (P/O Change B) Replace Figure 4-4, “Model 478A Thermistor Mount Assembly,” on page 41 with Figure A-8. Figure A-8 Model 478A Thermistor Mount Assembly (P/O Change B) Keysight 478A Operating and Service Manual...
  • Page 54 Appendix A Replace Figure 4-5, “Keysight Model 478A Printed Circuit Assy Wiring,” on page 42 with Figure A-9. Figure A-9 Keysight Model 478A Printed Circuit Assembly Wiring (P/O Change B) Keysight 478A Operating and Service Manual...
  • Page 55 This information is subject to change without notice. Always refer to the Keysight website for the latest revision. © Keysight Technologies 2008 - 2020 Edition 3, January 23, 2020 Printed in Malaysia *00478-90021* 00478-90021 www.keysight.com...

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