In this episode Shahriar tries to get a multi-stage Turbo Pump running. The unit comprises cylinder-based rouging pump into two stages of turbo pumps. The entire system is described with various interlock and controller mechanisms. The top blades of each pump are also shown.
The pump reached 10^-6 Torr fairly quickly but will likely need additional cleaning and long runtime to achieve anything below 10^-7 Torr.
In this episode Shahriar dives into the world of high-voltage circuit design. In order to appreciate the engineering involved in the design of a 40kV amplifier, various design techniques for power supplies and their applications are presented. This tutorial is organized as follows:
00:00 – Introductions
00:29 – Amplifier design specifications and challenges
03:18 – Typical high-voltage generation using transformers and its limitations
06:41 – Open-loop transformer high-voltage power supply for discharge tube use-cases
10:18 – Inaccurate HV power supply making precision isolation measurements with Fluke 1587 FC
12:39 – Stanford Research PS350 high-voltage DC power supply design and measurements
21:44 – Vitrek V74 HiPot safety tester design, applications and example breakdown measurement
27:01 – Architecture of a high-voltage amplifier circuit, circuit diagram and theory of operation
32:43 – Teardown & analysis of the Trek Model 20/20B +/- 20kV amplifier instrument
42:02 – Linearity and waveform measurements of the high-voltage amplifier instrument
46:26 – Making ultra-high voltage time-domain measurements using a capacitive divider
48:45 – Discharge tube response as a function of AC frequency & high-power sparks
50:12 – Concluding remarks
In this episode Shahriar repairs a faulty Agilent 3458A. These highly desirable multimeters have continued to climb in price in the past few years. The last time The Signal Path has repaired one of these units was back in 2018.
This instrument generates several errors both during power up as well as Auto Cal procedure. The error points to a failure in the OHMS measurement mode. Detailed instrument block diagram and schematics are examined. Measurements also show incorrect DC current sourcing during OHMS measurements and the associated circuits are closely analyzed. The problem is traced to a quad-comparator IC. Replacement corrects all problems during ACAL. The battery backup of the SRAM ICs are also replaced to eliminate non-volatile errors. The IC of the comparator chip is also extracted and examined under the microscope.
The repaired instrument performance is verified by using voltage, current and resistance standards.
In this episode Shahriar repairs an Agilent N9912A which flags several error messages after bootup. The instrument reports hardware time-outs and occasionally ADC clock source unlock condition. The second error is much more useful in debugging the unit.
The block diagram of the instrument is presented and several potential failures anticipated.
The teardown of the unit and analysis is also presented. After some troubleshooting, it becomes clear that the primary 30MHz TCXO has a broken internal connection. The unit is disassembled and new pins installed. After putting the TCXO back into the unit, the instrument return to full functionality. A few quick experiments verify that the FieldFox performs both CAT and SA modes correctly.
The Signal Path (TSP) is a science & electrical engineering video blog for industry professionals, researchers & students. TSP is a not-for-profit website dedicated to provide free education spanning a wide range of electrical engineering & science topics. Equipment reviews, tutorials and repair videos are posted regularly.
