??? 03/04/04 17:52 Read: times |
#65979 - RE: Solenoid operated Pneumatic valves Responding to: ???'s previous message |
Hallo Prahlad,
from mobile welding machines I know, that mechanical contactors are used for controlling protection gas (argon + etc.). Good mechanical contactors have a lifetime of 3 x 10**7 switchings. So, you can estimate how many years your product will work. On the other hand, solid state contactors are much more elegant, of course. Smaller, quiet, less control power. BUT: Solid state contactors are not fool proof! Most of them are susceptible to fast voltage changes across their contacts. If the voltage across contacts shows a change rate of more than 500V/µsec (this is a typical value), solid state contactor is firing itself! Means, solid state contactor is eroneously turned-on!! Such seltriggering can occur for instance, if the 100VAC supply has had a momentary power-down and turns-on again very rapidly. So, with solid state contactors you always need to take special care on filtering in order to remove glitches of higher slew rates than 500V/µsec. One very simple methode is to put a capacitor across contacts. But a right line filter will show much better results, of course. You could experiment with SC862110 from CELDUC, e.g. Is available from RS-components under "231-3566". Control voltage: 5-30DC, Contacts: 24-520VAC (0.1-400Hz), Imax = 25A, dv/dtmax = 500V/µsec. Makes contact at zero voltage, opens contact at zero current and is fabricated to be used with solenoid valves, beside others, of course. Kai |