PyVISA & Instrument Control with Python

PyVISA is a Python package that enables you to control all kinds of measurement devices independently of the interface (e.g. GPIB, RS232, USB, Ethernet).

As you might know, the programming of test and measurement (T&M) instruments can be real pain. There are many different protocols, sent over many different interfaces and bus systems (e.g. GPIB, RS232, USB, Ethernet).

For every programming language you want to use, you have to find libraries that support both your device and its bus system.

In order to ease this unfortunate situation, the Virtual Instrument Software Architecture (VISA) specification was defined in the middle of the 90's.

VISA is a standard for configuring, programming, and troubleshooting instrumentation systems comprising GPIB, VXI, PXI, Serial, Ethernet, and/or USB interfaces. Today VISA is implemented on all significant operating systems.

Simply put, computers are often used to communicate with measurement equipment to automate a measurement, and there are many ways to implement this communication.

While it is possible to communicate via the serial ports or USB ports using a low-level computer language, it is usually more convenient to use a high level language such as LabVIEW or Python to communicate with instruments. These languages can then also be used to manipulate the data and display it.

Some instruments implement the Virtual Instrument Software Architecture(VISA) which is a standard that gives the instruments plug-and-play capability. 

Programs that understand VISA (like LabVIEW or Python) can recognize which instruments are connected to the computer and communicate with them.

Usually this communication takes place by sending text strings to the instrument. A common format is called Standard Commands for Programmable Instruments (SCPI).

Anyway, some manufacturers do not follow these standards and it is necessary to install drivers to communicate with their instruments.

Note that for instruments that have a microprocessor and memory, it is often possible to upload a program to the instrument and then tell the instrument to execute this program. Popular programming environments for communicating with and controlling instruments are LabVIEW and Python.

Python is a high level programming language that is suitable for small and large projects. It has a large library, operates on many platforms, and is free to download. To communicate with instruments that support the VISA standard it is easy to use the PyVISA package as it allows you to communicate using a variety of interfaces such as GPIB, RS232, USB.

That is it for now. More to come later ⫸

(info source courtesy - https://www.tugraz.at/home)

Car Audio System & Power Ratings

Obviously, the most popular specification that consumers look at when purchasing a car audio amplifier system is its output power rating.

OK, this quick post is to help you get an overview of what the amplifier power rating means!

Basically, an audio amplifier system takes a small signal input and raises it in voltage and current to drive a low-impedance loudspeaker. Note that the more power you have, the more loudly you can play your car audio system before the signal going to the loud speakers distorts. 

And, the limit of how much power is required is determined by the power handling specifications of the in-car loud speakers ,their cone excursion limits and their distortion characteristics. 

An audio amplifier set up in a lab to measure power is typically connected to a power supply and a set of load resistors. Special test equipments are also used to measure the distortion characteristics of the output signal to determine the point at which you would hear the distortion.

The Consumer Technology Association (CTA) has established a standard for the power and signal-to-noise ratio measurements of car audio amplifiers called CTA-2006-B.

The specification states that power measurements are to be taken with the car amplifier powered with a DC voltage of 14.4V, and the measurement is taken into a specified load (Typically 4Ω) with no more than 1% total harmonic distortion and noise (THD+N) across the entire bandwidth of the amplifier.

Simply put, the audio amplifier must perform as well producing bass as it does high-frequency information, and the specified power rating cannot include large amounts of distortion.

What is the difference between continuous RMS vs. peak power?

And why does it matter? Read this PDF ↗

Finally, this post is just a snip from a BestCarAudio.com Magazine article published in 2019.

This is the LINK to the original article Understanding the Specs – Amplifier Power Ratings ⇱

See you next week ⪫

Ferroresonant Transformer

A Ferroresonant Transformer, also know as constant voltage transformer (CVT) is designed to achieve regulation with non-linear operation. It provides line regulation, reduce harmonics, and is current limiting.

In addition to providing above benefits, it also provides line isolation and some models come built in with additional output transient voltage suppression (TVS) mechanism.

There is no method in a conventional transformer for the regulation of the output against changing input voltages because it is designed to operate on the linear portion of the magnetization curve (below the knee).

A basic ferroresonant transformer consists of a core, a primary winding, two secondary windings - one for the load and one for the capacitor - and a magnetic shunt that separates the primary and secondary windings. The load regulation will be higher because of the inherent internal regulation of the transformer.

In other words, ferroresonant transformer uses a transformer core that is operated in saturation. So, a change of magnitude of flux density is relatively independent of the magnetic flux inside the core. This means, since the transformer core is operated under saturation, small change in input voltage do not cause any significant change in the output voltage.

Note that the secondary circuit of the ferroresonant transformer comprises of a resonant tank circuit. If the resonant tank circuit is not there, the output voltage will be a square wave with high harmonic voltage distortion. By adding the resonant circuit, a quasi-sine wave voltage can be obtained.

To sum-up, ferro-resonant transformer is a special lamination transformer. Sometimes it may be preferred as constant-voltage-transformer (CVT) or voltage stabilizer because it provides a relatively constant output voltage with less distortion using a wide range of input voltages. 

Benefiting from the features of regulated output, quasi-square waveform and wide input voltage range, ferroresonant transformer is widely used in power supply, voltage regulator, lighting, inverter, battery charger and other industrial tools.

In industry, ferroresonant transformers are used in application that could be negatively affected by voltage sags or voltage dips in the power system.

Keep note that a Constant Voltage Normal (CVN) transformer produces a square wave output, while a Constant Voltage Sinusoidal (CVS) transformer produces a sinewave output!

Thanks ◮  https://electroncoil.com https://voltage-disturbance.com https://www.shapellc.com → 

Power NTC Thermistors

This quick post is about Power NTC Thermistors & Inrush Current Limiting!

At the time of powering on an electronic device such as a switch-mode power supply, the device is charged with an instantaneous abnormal current with a high peak.

It is called an inrush current, and without protection, it may destroy a sensitive semiconductor device or have a harmful effect on the service life of a smoothing capacitor.

Power NTC thermistors are used as inrush current limiters (ICLs) to protect circuits of electrical and electronic devices against inrush currents easily and effectively.

Basically, NTC thermistor is a temperature-dependent non-linear resistor that employs special semiconductor ceramics with a negative temperature coefficient (NTC).

An NTC thermistor has a high resistance at room temperature, and when it is energized, it generates heat by itself and the resistance falls as the temperature rises.

With this property, it can be used as a current protection device to limit inrush currents.

See, the manner in which the resistance of an NTC thermistor decreases is related to a constant known in the electronics industry as beta, or ß. Beta is measured in °K.

In a nutshell, Power NTC Thermistors are made of a metal-oxide ceramic material in the form of ceramic discs that help provide protection against damaging inrush currents upon equipment startup and/or switching on.

As such, Power NTC Thermistors are commonly referred to as Inrush Current Limiters (ICLs) and help reduce downstream component damage.

NTC Thermistor General Information - Technical Overview (TDK) PDF ⇲

How to select NTC thermistors for inrush current limiting?

In practice, there are 3 major criteria for selecting the best NTC thermistor inrush current limiter, surge suppressor for an application:

• Rated resistance (R25)
• Maximum permissible continuous current under rated operating conditions (Imax, DC or RMS values for AC)
• Maximum capacitance CT to be switched

Read More & Stay Tuned https://amwei.com/how-to-select-ntc-thermistors-for-inrush-current-limiting/

Intermediate Frequency Transformer (IFT)

In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception.

Intermediate frequencies are used in superheterodyne radio receivers, in which an incoming signal is shifted to an intermediate frequency for amplification before final detection is done.

The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called heterodyning, resulting in a signal at the difference or beat frequency.

According to Wikipedia, perhaps the most commonly used intermediate frequencies for broadcast receivers are around 455 kHz for AM receivers and 10.7 MHz for FM receivers, some other frequencies can be used in special purpose receivers, though.

IF transformers or IF amplifier transformers are simply tunable inductors, usually with an integral fixed capacitor, and are typically used inside cheaper transistor radios. Mostly they are used as synchronously tuned filters because each stage is coupled by an active device.

In other words, an IF, or Intermediate Frequency, Transformer (IFT) is a tuned air core transformer used in just about all analog Superheterodyne receivers in past and current AM and FM designs.

Intermediate Frequencies (IF) have been standardized on the broadcast bands with 455 kHz used for AM and 10.7 MHz used for FM.

Most Superheterodyne receivers have two or more IFTs to increase signal gain and selectivity (selectivity is the ability of a radio receiver to focus on one broadcast while rejecting others that are close in frequency as the desired one).

Superheterodyne Radios take an incoming broadcast and convert it to an intermediate frequency using a process called Heterodyning.

Heterodyning is used as it is more efficient and cost effective to design a radio frequency (RF) amplifier for a small window of frequencies than to design one efficient across and entire broadcast band.

For the noobs, essentially there are two coils in an IFT usually (but not always) one above the other.

The IFT is tuned to the intermediate frequency (IF) of the radio which is the difference between the tuned signal being received and the local oscillator (LO) in the radio which usually runs at a higher frequency.

So if you are receiving a signal at 1500 kHz, the local oscillator could be running at 1955 kHz. The difference here is 455 kHz and this is what the IFTs will be tuned to. And to some extent, correct tuning of the IFTs will affect the audio signal quality in subtle ways. 

Put another way, in a traditional AM radio where the received signal is in the range 540 kHz to 1650 kHz, the local oscillator (which's in fact a variable frequency oscillator) signal is always a constant 455 kHz higher or 995 kHz to 2105 kHz.

Rather unsurprisingly, vintage medium wave (MW) AM radios often had double tuned IFTs. These old school IFTs do not have taps and therefore are high impedance devices that are intended for vacuum tube (valve) radios.

So, IFTs used in valve radios usually have tuned primary and secondary circuits whereas transistor radios usually have a single tuned circuit.

Therefore, an IFT for use with transistors will have one adjustment (the primary) and an IFT for use with valves will have two adjustments (the primary and the secondary).

More to come soon (hopefully) ◌⇲

(thanks to https://www.electronics-tutorials.com)

Neodymium Disc & Ring Magnets & Magnetization Directions

Neodymium rare earth magnets (NdFeb) vary in shape and size, and the different shapes each have their own corresponding magnetization direction patterns. 

All Neodymium magnets have both a north and south pole.

Becoming familiar with the magnetization direction of your magnets will help you determine which one is best for your project and which way it should be oriented so that it works most effectively.

Note that a magnet is strongest when one of its poles is touching the opposing surface. For example, an axially magnetized disc/ring magnet will work best when one of its fl at faces is flush against the flat opposite-polarity side of another disc or ring magnet.

Disc magnets can be either axially magnetized or diametrically magnetized. Axially magnetized disc magnets have the north and south poles on the large flat surfaces, while diametrically magnetized disc magnets have the north and south poles on the rounded sides.

Likewise, ring magnets can be either axially magnetized or diametrically magnetized. That is, axially magnetized ring magnets have the north and south poles on the flat surfaces, while diametrically magnetized ring magnets have the north and south poles on the rounded side.

Neodymium ring magnet is circular in shape with a hollow center. Besides the conventional axial magnetizing or diametrically magnetizing ring magnets, radially oriented ring magnet (uni-pole magnetized magnet) is also available. 

Note: Neodymium ring magnets are easy to corrode under humid environment and are necessary to cover with a protective coating.

⇲ Main Reference Source https://totalelement.com/blogs/about-neodymium-magnets/neodymium-magnetization-direction