In addition to performing tasks of amplification and switching, tubes can be designed to serve as display devices.
Perhaps the best-known display tube is the cathode ray tube, or CRT. Originally invented as an instrument to study the behavior of “cathode rays” (electrons) in a vacuum, these tubes developed into instruments useful in detecting voltage, then later as video projection devices with the advent of television. The main difference between CRTs used in oscilloscopes and CRTs used in televisions is that the oscilloscope variety exclusively uses electrostatic (plate) deflection, while televisions use electromagnetic (coil) deflection. Plates function much better than coils over a wider range of signal frequencies, which is great for oscilloscopes but irrelevant for televisions since a television electron beam sweeps vertically and horizontally at fixed frequencies. Electromagnetic deflection coils are much preferred in television CRT construction because they do not have to penetrate the glass envelope of the tube, thus decreasing the production costs and increasing tube reliability.
An interesting “cousin” to the CRT is the Cat-Eye or Magic-Eye indicator tube. Essentially, this tube is a voltage-measuring device with a display resembling a glowing green ring. Electrons emitted by the cathode of this tube impinge on a fluorescent screen, causing the green-colored light to be emitted. The shape of the glow produced by the fluorescent screen varies as the amount of voltage applied to a grid changes:
The width of the shadow is directly determined by the potential difference between the control electrode and the fluorescent screen. The control electrode is a narrow rod placed between the cathode and the fluorescent screen. If that control electrode (rod) is significantly more negative than the fluorescent screen, it will deflect some electrons away from that area of the screen. The area of the screen “shadowed” by the control electrode will appear darker when there is a significant voltage difference between the two. When the control electrode and fluorescent screen are at equal potential (zero voltage between them), the shadowing effect will be minimal, and the screen will be equally illuminated.
The schematic symbol for a “cat-eye” tube looks something like this:
Here is a photograph of a cat-eye tube, showing the circular display region as well as the glass envelope, socket (black, at far end of tube), and some of its internal structure:
Normally, only the end of the tube would protrude from a hole in an instrument panel, so the user could view the circular, fluorescent screen. In its simplest usage, a “cat-eye” tube could be operated without the use of the amplifier grid. However, in order to make it more sensitive, the amplifier grid is used, and it is used like this:
The cathode, amplifier grid, and plate act as a triode to create large changes in plate-to-cathode voltage for small changes in grid-to-cathode voltage. Because the control electrode is internally connected to the plate, it is electrically common to it and therefore possesses the same amount of voltage with respect to the cathode that the plate does. Thus, the large voltage changes induced on the plate due to small voltage changes on the amplifier grid end up causing large changes in the width of the shadow seen by whoever is viewing the tube.
“Cat-eye” tubes were never accurate enough to be equipped with a graduated scale, as is the case with CRTs and electromechanical meter movements. But they served well as null detectors in bridge circuits and as signal strength indicators in radio tuning circuits. An unfortunate limitation of the “cat-eye” tube as a null detector was the fact that it was not directly capable of voltage indication in both polarities.
In Partnership with Renesas Electronics
by Jake Hertz
by Jake Hertz
| 盛世美颜是什么意思 | ono是什么意思 | 北齐是什么朝代 | 脊髓损伤有什么症状 | 柔顺剂是什么 |
| 瘦人吃什么能长胖 | 79年属羊的是什么命 | nrc是什么意思 | 西瓜霜是什么 | bmi是什么 |
| 染色体xy代表什么 | 肺气不足吃什么食物可以补肺气 | dvt是什么意思 | ct是什么 | 大肠湿热吃什么中成药 |
| 肌酐测定是查什么 | 女属羊和什么属相最配 | 什么是乐高 | 脸发麻是什么原因 | 血管炎吃什么药最有效 |
| 月经提前了10天是什么原因dayuxmw.com | 莜面是什么面做的hcv8jop8ns5r.cn | from是什么意思hcv9jop8ns3r.cn | 人这一生什么最重要hcv8jop4ns5r.cn | 身上长很多痣是什么原因hcv8jop6ns1r.cn |
| 停职是什么意思hcv9jop0ns8r.cn | 什么米之乡hcv8jop6ns3r.cn | 牵连是什么意思wmyky.com | 嘴唇暗紫色是什么原因hcv9jop3ns1r.cn | 什么样的河流hcv8jop6ns3r.cn |
| 干水是什么hcv8jop8ns3r.cn | 黄片是什么hkuteam.com | 恨嫁什么意思hcv7jop9ns9r.cn | 蕃秀什么意思hcv8jop2ns9r.cn | 幽门螺旋杆菌是什么hcv8jop2ns9r.cn |
| kaiser是什么品牌hcv8jop4ns2r.cn | 星期天左眼皮跳是什么预兆dajiketang.com | 手上为什么会有小水泡hcv9jop5ns4r.cn | 淋巴发炎吃什么药好hcv8jop1ns9r.cn | 男人有霉菌是什么症状yanzhenzixun.com |
Not all of the figures appear in this article, for example, the schematic of the tube doesn’t appear.