TRIGGER 24 VDC VALVES WITH DIGITAL OUTPUTS

[rodriferfe]

Hi Guys,

I have some solenoid valves (24 V, 100 mA) I want to trigger them with the digital lines of my DAQ USB. As the digital lines are just 5 V I could amplify the voltage but in any case the current is too low to trigger them. I was wondering if there is something, like a switch that can be drived by the digital output in such a way that when it is actuated connect a 24 VCD power supply with the valve so it closes and when I stop applying the 5 V it is switched off. Electronics is not my background as you can see so I would appreciate if you could tell which is the best way to do this.

Thank you very much

[GerdW]

Hi rodriferfe,

I was wondering if there is something, like a switch

Yes, there is!

Electronics is not my background

You should read it up… 😄

There are SSR (solid state relais), which operate with just 5V/5mA at their input.

There are MOSFETs, which you can drive with a simple TTL output.

There are other options as well. Ask an electrician of your choice!

[rodriferfe]

Hi GerdW,

Yes googling I found that solid state relays is what I need, just trying to find which model will fit my needs. Any suggestion?

Thank you very much

[GerdW]

Hi rodriferfe,

you need to tell us which DAQ hardware you use!

There are devices capable of driving 20mA (standard TTL), while others only supply 2mA (low power TTL) - so there is no general recommendation possible!

With a standard TTL device you can google for "ssr 5V input".

With a low power device you rather should solder your own PCB with transistors…

[rodriferfe]

It is the 6218 USB DAQ, if I recall well the digital outputs are TTL 50 mA max. 

[GerdW]

Hi rodriferfe,

when you read the spec carefully you will see it provides 16mA per DO channel and 50mA for all DO channels…

16mA are ok to drive a SSR with TTL-compatible input. Just search for them…

[Ben]

What Gerd said !

Pheonix Contacts offer a lot of options. You have to make a choice based on both the control and the switched contacts. You have to know the voltage and curent of your DO lines and the same for the switched contacts as well as AC vs DC.

I like the ones with buit-in LEDs so I can check the state at a glance.

Digi-Key can help you find a good realy if you know the specs.

Ben

[AnalogKid2DigitalMan]

The ULN2003 is well suited for such applications if the valves are DC powered, see:

http://www.ti.com/lit/ds/symlink/uln2003a.pdf

-AK2DM

[RTSLVU]

Hwew are some basic circuits I posted for a simmilar question a few years ago.

You would replace the LED and resistor with your valve.

[AnalogKid2DigitalMan]

If you do use discrete transistors/MOSFETs/Drivers also add a reversed biased diode (1N4004 shouldd suffice) across the valve coil to absorb the back-EMF when power is removed from the coil. Not doing so may fry the discretes along with your DAQ and maybe the PC too. The ULN200x's have the diodes built in.

-AK2DM