In this episode Shahriar asks an AI LLM to solve problems from the final exam of a metrology & instrumentation course intended for electrical engineering graduate students.
We also do some experiments to verify the theory from one of the questions. Let’s see how well AI can tackle these problems!
In this episode Shahriar repairs a Keysight 53230A frequency counter with an unusual problem. The instrument reports OVERLOAD for both high & low thresholds on both Channel 1 & Channel 2 with or without an input signal. With this problem, the instrument also fails self-test.
There is no schematic or even a block diagram for this instrument. But since the unit is equipped with both the Microwave Pulse Measurement as well as the 15GHz Microwave input option (as Channel 3), it is certainly worth repairing. Channel 3 of the instrument is fully functional, which is a good sign for the health of the latter DSP portion of the unit.
Teardown reveals two parallel & identical Channel 1 & Channel 2. The circuits are examined in details and the primary comparators are identified. After some testing, it becomes clear that the comparator thresholds are controlled via some ADI DACs which are maxed out due to inactivity at the output of the comparators. Interestingly, the latch inputs ports of the comparator ICs are also controlled by a different DAC. This is the first part which is in common with both channels. After replacing this DAC, the instrument no longer reports the OVERLOAD error.
The instrument is also upgraded with an OCXO which should bring much better frequency stability. The unit is then calibrated against a Rubidium standard. The microwave pulse measurement is demonstrated first using a R&S SMBV100B Vector Signal Generator & Tektronix MSO-6B Mixed-Domain Oscilloscope. The Keysight 53230A is easily able to measure pulse duration, repetition as well as the carrier frequency. The frequency counter's trend chart, histogram & other advanced DSP functions are also demonstrated.
In this episode Shahriar re-traces history and measures an important characteristics of a fundamental sub-atomic particle: the charge to mass ratio of an electron.
This experiment, first performed in 1897 by J.J. Thomson, changed physics by showing that atoms are indeed made of further sub-atomic particles through the discovery of electrons. We build a setup using a pair of Helmholtz coils, a cold-cathode vacuum tube driven by a multi-kV DC power supply & careful measurements of the beam deflection angle. The theoretical foundation of the experiment is described in details.
The measured e/m ratio is compared with the NIST established number with great agreement. The historical impact of the work of J.J Thomson & Robert Milikan (measuring the charge of an electron) are also presented.
The two winners of the giveaway are:
@nicolasblomstrand2912 (YouTube)
Robert S. (Patreon)
In this episode Shahriar dives into the concept of a capacitance bridges. In particular, the Andeen-Hagerling AH2500A Ultra-Precision Capacitance Bridge:
The theory of operation is explained in details alongside a comparison with more traditional LCR meters. A simple replica transformer-based bridge circuit is also used to demonstrate the principle operation using a Zurich-Instruments MFIA lock-in amplifier. The teardown of the unit provides further insight into the engineering design of the instrument.
The capacitance bridge is also used to measure small shifts in a parallel plate capacitor. Furthermore, a complete set of air capacitor standard modules are calibrated & adjusted using the bridge as a standard.
In this episode Shahriar take a look at a broken Chub. These instruments are able to measure PRTs, Thermistors as well as other resistive based thermometers. They can also be quipped with thermocouple reader modules.
This specific instrument has a blown fuse and draws an excessive amount of current. The first problem is a faulty 5V DC/DC converter. Although changing the IC does resolve the 5V power supply problem, it is likely that the failure has also caused excessive voltage to appear across the unit. There is no activity from the microprocessor. After replacing the processor and re-programming the EEPROM, the unit is up and running. A few experiments with various sensors and precision resistors verified the functionality of the instrument.
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.
