Audio Technologies

Text Box: Copyright 2012 Audio Technologies, Miltiadis Logothetis Laboratory, All Rights Reserved.
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# Two 800VA transformers # AC voltage output indication # 240VAC limiter # Slow rise circuit # VAC mains DC stopper

 

Any transformer, whether used to transfer signals or power is isolating, as the primary and secondary are not connected by conductors but only by induction.

However, only transformers whose primary purpose is to isolate circuits opposed to the more common transformer function of voltage conversion are routinely described as isolation transformers.

The MIT-1K6 isolation transformer is used to transfer electrical power from a source of alternating current (AC) power to some device, isolating the powered device from the power source.

The MIT-1K6 provide galvanic isolation and is used to protect against electric shock, to suppress electrical noise in sensitive devices and to transfer power between two circuits which must not be connected together.

It blocks interference caused by ground loops.

It has electrostatic shields so can be used for power supplies for sensitive equipment such as Hi-fi, computers or laboratory instruments.

Given this function, is built with special insulation between primary and secondary, and is tested and specified to withstand a high voltage between his windings from 400 to 3000 volt.

The MIT-1K6 is designed with careful attention to capacitive coupling between the two windings.

The capacitance between primary and secondary windings also couple AC current between them.

A grounded Faraday shield between the primary and the secondary greatly reduces the coupling of common-mode noise.

The grounded shield prevents capacitive coupling between primary and secondary windings.

A balanced secondary with an earthed center is used.

It reduces earth leakage in equipment used in wet locations.

The maximum voltage above earth is halved, reducing the risk of shock.

With the MIT-1K6 as there is no conductive connection between transformer secondary and earth, there is no danger in touching a live part of a circuit while another part of the body is earthed.

The outputs of the MΙT-1K6 provide the connected audio components with clean balanced power.

The MIT-1K6 optional can be ordered at half power (800VA), with one toroidal transformer as MIT-0K8.

# Δύο 800VA μετασχηματιστές # AC ένδειξη τάσης εξόδου # 240VAC περιοριστής # Κύκλωμα αργής εκκίνησης # VAC δικτύου DC stopper κύκλωμα

 

Οποιοσδήποτε μετασχηματιστής, είτε χρησιμοποιείται για τη μεταφορά σημάτων είτε για ισχύ απομονώνει, καθώς το πρωτεύον και δευτερεύον δεν είναι συνδεδεμένα με αγωγούς, αλλά μόνο με επαγωγή.

Ωστόσο, μόνο οι μετασχηματιστές των οποίων πρωταρχικός σκοπός είναι να απομονώσουν κυκλώματα σε αντίθεση με την πιο κοινή λειτουργία του μετασχηματιστή μετατροπής τάσης, συνήθως περιγράφονται ως μετασχηματιστές απομόνωσης.

Οι μετασχηματιστές απομόνωσης του MIT-1K6 χρησιμοποιούνται για τη μεταφορά ηλεκτρικής ενέργειας από μια πηγή εναλλασσόμενου ρεύματος (AC) σε κάποια συσκευή, απομονώνοντας την τροφοδοτούμενη συσκευή από την πηγή ενέργειας.

Ο MIT-1K6 παρέχει γαλβανική απομόνωση και χρησιμοποιείται για την προστασία ενάντια στην ηλεκτροπληξία, για να καταστείλει ηλεκτρικούς θορύβους σε ευαίσθητες συσκευές και για τη μεταφορά ηλεκτρικής ενέργειας μεταξύ δύο κυκλωμάτων που δεν πρέπει να συνδέονται μεταξύ τους.

Αναστέλλει παρεμβολές που προκαλούνται από βρόγχους γειώσεων.

Διαθέτει ηλεκτροστατική θωράκιση, ώστε να μπορεί να χρησιμοποιηθεί για τροφοδοσία τροφοδοτικών ευαίσθητων εξοπλισμών όπως Hi-fi, υπολογιστών ή εργαστηριακών οργάνων.

Με δεδομένη αυτή τη λειτουργία, είναι κατασκευασμένος με ειδική μόνωση μεταξύ πρωτεύοντος δευτερεύοντος και δοκιμάστηκε και ορίστηκε να αντέχει σε υψηλή τάση μεταξύ των πηνίων του από 400 έως 3000 βολτ.

Ο MIT-1K6 είναι σχεδιασμένος με ιδιαίτερη προσοχή στη χωρητική σύζευξη μεταξύ των δύο περιελίξεων.

Η χωρητικότητα μεταξύ πρωτευόντων και δευτερευόντων περιελίξεων ζευγαρώνει και το AC ρεύμα μεταξύ τους.

Μια γειωμένη θωράκιση Faraday μεταξύ πρωτεύοντος δευτερεύοντος μειώνει σημαντικά τη σύζευξη του θορύβου common-mode.

Η γειωμένη θωράκιση αποτρέπει χωρητική σύζευξη μεταξύ πρωτευόντων και δευτερευόντων περιελίξεων.

Ένα ισορροπημένο δευτερεύον με μια γειωμένη μεσαία λήψη χρησιμοποιείται.

Μειώνει τις διαρροές προς τη γη εξοπλισμών που χρησιμοποιούνται σε υγρές περιοχές.

Η μέγιστη τάση πάνω από τη γη είναι η μισή, μειώνοντας τον κίνδυνο ηλεκτροπληξίας.

Με τον MIT-1K6, καθώς δεν υπάρχει αγώγιμη σύνδεση μεταξύ δευτερεύοντος του μετασχηματιστή και της γης, δεν υπάρχει κίνδυνος επαφής με την φάση ενός κυκλώματος ενώ ένα άλλο μέρος του σώματος είναι γειωμένο.

Οι έξοδοι του MΙT-1K6 παρέχουν στις συνδεδεμένες συσκευές ήχου καθαρή ισορροπημένη ισχύ. 

 

MIT-1K6  SPECIFICATIONS

TOTAL POWER: 1600VA@230VAC.

INPUT: 230VAC, 1600VA maximum.

PROTECTIONS: 240VAC limiter, slow rise circuit, mains VAC  DC stopper circuit.

OUTPUTS: 6x Berker schuko sockets, each 2000W/230VAC.

DIMENSIONS: 37x22x12cm.

WEIGHT: 16kg

MIT-1K6 mains isolation transformer

Rounded Rectangle: MIT-1K6 pictures###

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TOTAL POWER: 800VA@230VAC.

INPUT: 230VAC, 800VA maximum.

PROTECTIONS: 240VAC limiter, slow rise circuit, mains VAC  DC stopper circuit.

OUTPUTS: 6x Berker schuko sockets, each 1000W/230VAC.

DIMENSIONS: 37x22x12cm.

WEIGHT: 9kg

MIT-0K8  SPECIFICATIONS

Transformer noise

Audible noise is an effect primarily originating from the phenomenon of magnetostriction.

Magnetostriction is the slight change of length exhibited by a ferromagnetic object when magnetized.

The familiar hum heard around large power transformers is the sound of the iron core expanding and contracting at 100Hz, that is twice the system frequency of 50Hz in Europe, one cycle of core contraction and expansion for every peak of the magnetic flux waveform, plus noise created by mechanical forces between primary and secondary windings.

Again, maintaining low magnetic flux levels in the core is the key to minimizing this effect which explains why ferroresonant transformers, which must operate in saturation for a large portion of the current waveform, operate both hot and noisy.

Another noise producing phenomenon in power transformers is the physical reaction force between primary and secondary windings when heavily loaded.

If the secondary winding is open circuited, there will be no current through it, and consequently no MMF or Magneto-Motive-Force produced by it.

However, when the secondary is loaded, i.e. current is supplied to a load, the winding generates an MMF which becomes counteracted by a reflected MMF  in the primary winding to prevent core flux levels from changing.

These opposing MMFs generated between primary and secondary windings as a result of secondary load current produce a repulsive, physical force between the windings which will tend to make them vibrate.

In our Laboratory we consider these physical forces in the construction of the winding coils and core materials selection, to ensure there is adequate mechanical support to handle the stresses.

Only under very heavy load conditions, these stresses may be great enough to cause audible noise to emanate from the transformer.

Voltage regulation considerations

The output voltage of a transformer varies some with varying load resistances, even with a constant voltage input.

The degree of variance is affected by the primary and secondary winding inductances among other factors, not the least of which includes winding resistance and the degree of mutual inductance, or magnetic coupling, between the primary and secondary windings.

For power transformer applications, where the transformer is seen by the load ideally as a constant source of voltage, it is good to have the secondary voltage vary as little as possible for wide variances in load current.

We always carefully measure of how well a power transformer maintains constant secondary voltage over a range of load currents.

That is called the transformer's voltage regulation.

We calculate it from the following simple formula.

Regulation percentage % = E no load - E full load / E full load

Full load means the point at which the transformer is operating at maximum permissible secondary current.

The operating point will be determined primarily by the winding wire size, i.e. the amperes capacity, and the method of transformer cooling.

 

Transformer final design

Our transformers are well designed in order to achieve acceptable power coupling, tight voltage regulation and low exciting current distortion.

They are designed to carry the expected values of primary and secondary winding current without any trouble.

This means the winding conductors are made of the proper gauge wire to avoid any heating problems.

They have perfect coupling with no leakage inductance, perfect voltage regulation, perfectly sinusoidal exciting current, no hysteresis or eddy current losses and wire thick enough to handle any amount of current.

They have windings well insulated from the iron core and each sufficiently insulated from the other, in order to maintain the appropriate electrical isolation.

Among other measurements and tests always we make a frequency  transfer analysis with a spectrum analyzer.