Signs of the Times - July 2013 - (Page 26)

LIGHTING TECHNIQUES By Marcus Thielen Marcus Thielen is a physicist and lighting-industry consultant from Duisburg, Germany. Electronic Neon Power Supplies They’re not as simple as one might suspect. dead. However, neon-glass shops are reporting increasing work. Sign customers probably recognize neon as unique in its beauty, with long-time endurance in outdoor conditions. In contrast, in many new (outdoor) installations, I do see electronic neon power supplies (EPS) being used instead of magnetic, core-andcoil transformers. But EPS use can produce some trapdoors, so I’ve compiled some technical facts on the electronic powering of neon. EPS isn’t an invention of the semiconductor age (Fig. 1), and gas-discharge lamps advantageously powered by high-frequency electrical currents date back to Nicola Tesla. Neon tubes were even used to detect radio waves long before the vacuum electronic tube was invented (Fig. 2). Powering neon tubes with high frequency offers the benefit of a lower starting voltage, compared to a main’s frequency. In the past two decades, modern semiconductor electronics have produced a generation of smaller and cheaper, high-frequency, electrical Photo credit: Krypton Neon, LIC, NY Some voices to see)pronounced have (or would like neon already Fig. 1: EPS (flow effect) using vacuum tubes built in the early 1960s currents, i.e., competition for standard neon transformers. As I recently stated (see ST, March 2013, page 30), the higher the frequency, the smaller the inductors become for an equal power level. But here, the problem with high voltage, and, thus, neon supplies, starts. Fig. 2: A neon tube as a sensitive detector for high-frequency currents (left), right: discharge with high frequency in said tube (top), without high frequency (bottom). Patent by Zenneck (1892), taken from: Augusto Righi: Telegraphy Without Wires, 1903 26 SIGNS OF THE TIMES / JULY 2013 / www.signweb.com Dielectric strength (the resistance against electrical breakthrough, i.e., arcing) is reduced at higher frequencies, thus larger spacings and thicker insulation are required for the same voltage - so getting smaller in size has limited value, unless new insulation materials are employed. Many early EPS manufacturers learned this the hard way. EPS’ major technical problem is that neon tubes require a constantcurrent power source (see ST, May 2012, page 30). The current can be limited by several means, but, to avoid losses in neon transformers, the current is usually limited by the inductance of the secondary windings and a magnetic shunt in the core (see ST, June 2006, p. 28). However, with inductively limited currents, any capacitance in the highvoltage circuit neutralizes its function. In the worst case, coil inductance and external-circuit capacitance resonate on the operating frequency, which immediately destroys the power supply and the neon tube http://www.signweb.com

Table of Contents for the Digital Edition of Signs of the Times - July 2013

Signs of the Times - July 2013
Contents
ST Update
Technology Update
Vinyl Apps
Strictly Commercial
Lighting Techniques
The Moving Message
Technology Review
Technology Review
Design Matters
New Products
Vehicle Graphics Contest Entry Form
Public Displays of Affection
Electric-Sign Company 1 on 1’s
Screenprinting for Signmakers
A Century of Going Places
Industry News
Advertising index
Editorially speaking

Signs of the Times - July 2013