3 Zone Tube Furnace - what hardware do I need?

[Sonderval]

Hey folks,

Currently working on a 3 zone tube furnace that I want to automate via Labview (I currently have it set up to use a PID device). Just need to be sure I'm picking the right DAQ card  (and related signal conditioners) for this project and was hoping you guys could point me towards the correct product.

So we have a 3 zone furnace, each zone powered by a thyristor (the old Eurocube 424 models), The input for these guys is 0-10v. Each zone has an associated thermocouple, type K, that would need to be monitored. The whole thing is to be driven by a PID algorithm, which I'm sure Labview can handle.

I also need a 4th input for a another type k thermocouple. Looking to keep this relatively cheap too!

Any thoughts on what I'd need?

[JamesC]

Hi Sonderval,

Having a look at the DAQ product chooser page, I have come up with a short list for you.

I would think of using the PCI-6229 with a SCB-68 as this has an on-board CJC source for your thermocouples, so you will have 5 Analogue inputs, which means you can read in the analogue inputs at 250KS/s divide by 5 channels = 50KS/s per channel.
If that is fast enough for you this will be a good card as it  is a 16 bit card and the minimum input range is -200..200 mV, so matched quite well for a K-type thermocouple, so you should be ok for signal range. Also this card has 4 Analogue Outputs that will run at an update rate of 833KS/s, so more than fast enough for the PID you will be doing on the card. The downside is you will need 2 cables SHC68-68 and 2 terminal blocks either 1 SCB-68 or BNC-2120 and 1 CB-68 for the 2 additional output channels. This really ups the price, however you don't want to be tempted wit a USB solution. You could get a USB-6229 card however this does not have the cold junction compensation, but more importantly, USB is not the best bus for PID control, as you do not have the speed of the PCI bus or DMA transfers for single point updates. USB devices have a large latency to actually output a value. This latency can normally be ignored if you are streaming data because you have the initial latency and then all the data follows with no latency between points.
If however you do single point update (like PID control) then you have latency for every point of data you send and receive.

Regards
JamesC
NIUK and Ireland

Message Edited by JamesC on 10-17-2007 11:15 AM

[AnalogKid2DigitalMan]

You need safety!

Detection of open or disconnected thermocouples.

Separate over temperature safety switches to disable furnace directly.

What if OS or pogram locks up while applying power to the furnace?

Yes, LabVIEW application is cool but why can't off the shelf hardware controls be used?

Message Edited by AnalogKid2DigitalMan on 10-17-2007 01:35 PM

[Sonderval]

Cheers for the advice James.

Regarding that PCI card, you said I'd need 2 cables, yet the card only seems to support one. Am I missing something?

[JamesC]

Hi Sonderval,



Regards
JamesC
NIUK and Ireland

Message Edited by JamesC on 10-22-2007 02:28 PM