VISA read error happen but OK after restart computer

[Peter_liang]

When I read Gossen programmable power supply voltage with labview driver, it seems not stable. It read from windows USB port connect to power. When I run this without connecting other equipment, it seems OK. But when I connect another module share system variable, VISA read fail time out happen after a few times run . When I restart computer, it can work.

[Peter_liang]

当我用NI去读gossen可编程电源的电压和电流时， 循环超过一定次数后，总是会报错VISA read 超时。

请问可能是什么原因？

这个时候错误显示出错在如附件的读电压或者读电流vi，刚开始的COM口设置是COM9。 但是出错时，COM口变为COM1。

似乎是COM口的值在运行中变了。