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发表于 2009-11-5 16:26:00
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来自: 中国广东广州
关于数字量模块说明中的 "Lamp load" 是什么含意
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# |4 ?4 S( d$ N描述:
+ U+ [# d9 x( u8 Q在数字量输出的负载说明中有恒定值的阻性负载, 灯负载和感性负载。 在数据表中的这些值涉及到每个应用中的数字量输出。 ( d3 i! {, _$ q
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• 阻性负载
) l, d) u! B* O; e3 y, N: g& N 恒定的阻性负载的特性一般是在技术数据中以最大输出电流(当信号为1时)的说明来表示的。 ; s6 ?) L! [+ F# l
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• 灯负载# C$ J* ~* K* ^# a! Q
在使用灯负载时要考虑到灯的接通电流是额定工作电流的n倍。灯丝升温会导致阻抗迅速增大。灯负载在数据表中的特性以瓦特数来表示。这就意味着比产品在额定电压乘以允许输出电流所得功率低。高的接通电流导致了灯负载的最大开关频率要比恒定的阻性负载大约低10倍。因此,对于数字量输出只能连接总的额定瓦特数低于标定的灯负载的灯。 LED 指示灯不受影响,等同于阻性负载。 : v3 l( a# {" ]0 D; b/ t# u
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• 感性负载& j2 U6 B" d* o' o
如果使用感性负载,负载的阻抗(继电器线圈,接触器)大小依靠数字量输出的开关频率。因此,它允许的开关频率要比恒定的阻性负载的低很多,这样可以确保继电器开关的可靠性。这是因为感性负载电路要通过其保护电路将关断时产生的感应能量释放。 如果开关频率过快,关断电流能量不能被充分释放,结果导致输出继电器不能被关断。例如:在没有保护电路时,数字输出电子晶体管上就可能产生浪涌电压而损坏模块。9 c2 G/ i3 M6 R# ?' D, N2 K5 p
& b6 u3 b6 L) n注意:
5 [2 ]' H" k5 F9 N" c为防止过载必须注意模块的最大输出电流。 8 b! y( T0 e9 A! Z% @( ~
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条目号:24176167 日期:2006-12-19
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, j" h" _' w% k# eDescription:3 M( b/ n# \. C6 i! w
In the load specifications of digital outputs a distinction is made between constant ohmic load, lamp load and inductive load. The values in the data sheets refer in each case to one digital output.
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• Ohmic load. ]! g, l7 A# p% ]
The load capacity at constant ohmic load is usually characterized in the technical data by the specification of a maximum output current when the signal is at "1". ' j, @. E( a% h3 z+ a3 z
4 x7 n d3 x. Z2 u; Y • Lamp load
! h# `/ H* [8 O6 U8 N9 @! L- g The specification for the lamp load allows for the fact that the switch-on current of a filament lamp is n times greater than the rated current. The resistance only rises sharply as a result of the filament heating up. The lamp load is characterized in the data sheets by a wattage specification. This is significantly lower than the product of rated voltage times permissible output current. The high switch-on current of a filament lamp is also responsible for the fact that the maximum switching frequency is lower by approximately a factor of 10 than at constant ohmic load. Therefore, you may only connect filament lamps to a digital output that have a total rated wattage that is lower than the specified lamp load.) Y: h e; U( }# |
LED lamps are not affected. They are treated like an ohmic load. / E0 L; p* C: u$ e
# j; c* U* z5 U8 l • Inductive load
% J P, u% [7 h7 P' Q- q; s4 K In the case of inductive load, the impedance of the load (relay coil, contactor) depends on the switching frequency of the digital output.2 J; i- E9 s2 B) O
Therefore, here too the permissible switching frequency is a lot lower than that at constant ohmic load in order to ensure reliable switching of the relay. This is due to the discharge of the inductivity by the interrupting current via the protective circuit. If the switching frequency is too high, the interrupting current does not abate sufficiently. As a result, the relay at the output will not switch off, for example. Without a protective circuit, a voltage surge may occur at the power transistors of the digital output, resulting in the module being damaged or destroyed.. }5 p+ a/ t3 L& D; ?
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% A* h7 R6 I, c( P4 ]: j+ DNote:- W1 E i* [* r- v# `, B4 V
To prevent overloading the module you must also pay attention to the maximum total current of the outputs. $ L' k- S6 e$ W# ^2 \. A( h/ ^ ?
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Entry ID:24176167 Date:2006-11-29 |
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