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报警系统应具有防止传输线短路、断路、串接和并接负载的功能,这已列入国家标准。 一般的解决办法是在探头内串入电阻XR;如图1.探制台检测Ux的值,Ux的不同值对应不同的报警状态。这种方法可以有效解决短路和断路的干挠,但存在两个问题: 1.如果系统参数选择不当,罪犯就可以找到一个合适的电阻r,并联到传输线上,使报警器失效。例如系统参数选择x=3;U=5v;Ux的报警范围为±0.5V,那么选择r=5.342R,在探头动作前后,Ux的变化为±0.46V<±0.5V,从而使报警器失效。 2.如果在传输线上并一个正常电压,那么无论探头动作与否,Ux保持不变,报警器也失效。
Alarm system should have to prevent the transmission line short circuit, open circuit, series and parallel load function, which has been included in the national standard. The general solution is to string resistance XR into the probe, as shown in Figure 1. The probe detects the value of Ux and the different values of Ux correspond to different alarm states. This method can effectively solve the problems of short circuit and open circuit. However, there are two problems: 1. If the system parameters are not selected properly, criminals can find a suitable resistor r in parallel with the transmission line to disable the alarm. For example, the system parameter selection x = 3; U = 5v; Ux alarm range of ± 0.5V, then select r = 5.342R, before and after the probe moves, Ux changes ± 0.46V <± 0.5V, so that the alarm failure . 2. If the transmission line and a normal voltage, then whether the probe action or not, Ux remains unchanged, the alarm fails.