Temperature control by a digital output

[jas1991]

By the way, since you have seen the LabVIEW code I posted, would you be able to tell me they have used an Analog output port instead of a Digital Outpot port as we only want the relay to either turn on/off the heating tape. I don't know it has been wired like that.

Regards

[apok]

---

@jas1991 wrote:

By the way, since you have seen the LabVIEW code I posted, would you be able to tell me they have used an Analog output port instead of a Digital Outpot port as we only want the relay to either turn on/off the heating tape. I don't know it has been wired like that.

Regards

---

• Q:would you be able to tell me they have used an Analog output port? A: it is in plain site on the block diagram, hint: physical channels

as a student...has your instructor taught you LabVIEW basic? and as an engineer..has he taught you about requirements, specifications, implementation?

[jas1991]

I am a researcher, kinda student and I know the basics of LabVIEW, but I just was confused when I saw that in that LabVIEW file the output of the relay is an Analog, whereas I thought that it should be a digital, therefore I didn't know how should be well connected.

Thanks

[AnalogKid2DigitalMan]

That Powerex unit is not a relay per se, it is a Darlington power module with an isolated input. It's minimum base current looks to be 0.1A, way more than a digital output alone can provide, let alone get into the range of output saturation.

http://www.ineltron.de/english/powerex-data/ks224510.pdf

Here is an example of a traditional SSR module:

http://www.alliedelec.com/images/products/datasheets/bm/TYCO-ELECTRONICS/70198612.pdf

Their drive current (15mA) is still above what the digital output can supply, so you would need a buffer or driver between the DAQ digital output and the input of the SSR.

DAQ digital output >> buffer >> SSR input. (-) input of SSR goes to the DAQ GND.

Then one side of the SSR output goes to to 120VAC line (black), the other side to the heater tape and the other side of the tape to 120VAC neutral (white).

There are SSR that require just a few mA of input current, but I don't have time to search for one. Another option would be an opto or photo MOSFET relay for AC applications.

-AK2DM

[jas1991]

Thank you very much AK2DM!

However I have some questions regarding your reply.

When you mean by "you would need a buffer or driver between the DAQ digital output and the input of the SSR", what is the exactly reason for that?

As you have seen in one of the attachements, I have a power supply which is mainly a wall socket, so how would be the most safest way to connect the black wire to the output of the SSR?

Also in the LabVIEW file I attached at the beginning they are using an Analog Output for their Relay Output and you are suggesting about a Digital Output for that, I agree with you but, why don't they use it instead in their program?

Regards

[AnalogKid2DigitalMan]

A buffer or driver is needed because the maximum current the DAQ digital output can supply is ~8mA (read the specs). The SSR requires 15mA to power the input section.

Here is an example of a relay driver (ULN2003), typically used with electromechanical relays, but also be used to boost the current drive capacity of a digital ouput (up to 500mA) and would also work with a SSR.

http://www.st.com/web/en/resource/technical/document/datasheet/CD00001244.pdf

The program is using an analog ouput, but it is only ouputting 0 volts for OFF and 3V for ON. Again, the analog output is limited to 5mA of current so again a buffer is needed. You could still use it with the ULN2003 and SSR combo.

I suspect an analog ouput was used because the 6009's digital outputs are pulled high to 5V via a 4.7Kohm resistor. When the PC is powered up before the vi is ran, it may turn the heater ON.

SSR's typically use captive screw terminals to terminate the wire connection, so simply screw the wire to the terminal.

-AK2DM

[jas1991]

Here I am attaching you the scheme they used for the .vi file I attached. I feel I know more or less how I should do the wiring, but looking at it, seems there are less components than you mentioned. I don't know if there's another proper scheme of what you have described me.

Thanks

[AnalogKid2DigitalMan]

Looks like they were able to get away with driving the SSR directly from the DAQ card output.

Just copy how it is wired in that picture, you should be good to go. And don't let the magic smoke out!

-AK2DM