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/