What kind of DAQ do I need?

[boomer8]

Hello! I am a student and very new to this and am still getting familiar with the basics. I am working on a project with a pump and sensors.

I will have multiple sensors:

Temperature - T-type thermocouple, OMEGA HTQIN-18U-4 (2 or 3 of these)

Pressure - Pressure transducer, PCB 105C (2 or 3 of these)

Flow Rate - UFM TM0100-N (only 1)

My understanding is that the temperature and pressure sensors should be fairly general for the DAQ but I am concerned about the flow meter. It has a "Standard Magnetic Sine Wave" as the output listed on the specs... this has led me to believe that I will need a multifunction DAQ. Is this true?

Also, we want to program the DAQ to automatically shutoff the pump at certain pressures and temperatures. Is this possible?

Any help would be greatly appreciated!! Thank you. 

[mdwebster]

You're going to want a signal conditioner for that flow meter.  Trying to interpret the sine wave pickup is going to be difficult without an in-depth understanding of the device.  With a conditioner (what they call a 'control box'), like the FML250-P or P4, it will translate the flow to a pulse train or a 4-20mA output.

You can pick up the pulse train on a timed digital input, or the 4-20mA on a voltage input with the help of a 250 ohm 'translation' resistor. Or you could go straight to a 4-20mA cDAQ module, but that might be overkill if you're watching a budget.

The ICP (IEPE) pressure transducers are also going to need some conditioning before you can read them using a standard DAQ, or you're going to need an IEPE module or card (PCI-4462, NI-9234), but those tend to be quite expensive.

The thermocouples you can read with a standard DAQ card, but they're very low mV level signals, so your accuracy isn't going to be super great, and depending on the DAQ you may or may not have CJC correction.  Once again, you can get custom modules for this, like the NI-9210.  Those tend to be fairly reasonable, at least in comparison with the other devices I've mentioned.

And lastly, yes, you can definitely have a program that shuts off your pump under certain conditions.  Depending on how fast and reliable you need the response to be this can be done on a PC (slow ~1 second response time, not 100% reliable due to potential for Windows crashing, virus-scanning, or rebooting after an update) or a real-time system (much faster response time and nearly 100% reliable once programmed properly).  You just need a circuit to interface with the pump controller as most DAQ cards only have a 5V TTL output (but again, you can get custom modules that can switch 24V signals).  So you normally would use the DO to an output translation module (opto-22, dataforth, power-io) that would be used to throw a relay to the pump power.

[crossrulz]

I would be tempted to go with a cRIO.  You could probably get away with the 904x series controllers as they can use DAQmx.  There are then modules to handle the IEPE, thermocoupler, and 4-20mA signals.  You can then get another module for whatever DIO you need for the pump control/shutoff.

[boomer8]

This looks like a good option... do you suggest it because it is more simple or cheaper? With the modules, it seems it would be about the same price as the other option mentioned. 

I am looking at the modules and I am wondering if I would need 3 different ones for each sensor type?

thank you!

[boomer8]

WOW thank you so much for this info! After I read this, I feel like there is so much more that I need to figure out. I am going to reach out to my pressure transducer manufacturer to ask if they have a solution to the signal conditioning problem.

Thank you!

[mdwebster]

Unless you need those particular transducers due to accuracy or response speed or range, you can certainly get pressure transducers that give 0-5V or 0-10V outputs natively, same with the flow meter (thought 4-20 isn't that hard to read using a voltage input using a scaling resistor as mentioned earlier).  You can also get standalone thermocouple conditioners that linearize, CJC compensate, and amplify the thermocouples to a higher voltage output.  Then you could just have a cheap multifunction USB DAQ handle everything.  It really depends on what the requirements are and what your budget is.  Lots of variables.  Welcome to engineering ... 🙂

[sfrosty]

You can read about Thermocouples here:

https://www.ni.com/en-us/innovations/white-papers/16/temperature-sensor-basics.html

[boomer8]

I have decided to go with your suggestions!

Unfortunately yes we do need that specific pressure transducer. 

So we plan to go with:

Pressure:

PCB 105 C (pressure transducer) and the NI-9234 (IEPE Module)

Temperature:

Omega HTQIN-18U-4 (thermocouple) and NI-9210 (module)

Flow:

UFM TM0100-N (Flow meter), UFM FML250-P4 (signal conditioner) and NI-9203 (4-20mA cDAQ)

As far as the programmable shutoff goes, I am looking at the Opto22 GRV-OVMALC-8. Do you think this would be sufficient? 

Thank you in advance! I really appreciate your help.

[mdwebster]

That sounds good for modules.  You also need a backplane for those, FYI.  Like a CompactDAQ 4 slot chassis.

I've never used the Opto22 GLV components, but that looks like an analog output module for their 'groov EPIC' backplanes.

I was thinking more like an ODC5 or ODC5A that will change a TTL output into a switch for the pump power, but I don't know how you were planning on turning off or controlling the pump.  Of course, you also need a TTL Digital output on the NI side, but those are cheap, like an NI 9401.

You need backplanes (little circuit board carriers), for those.  If you just need the one, you might look at a DIN rail output module from Crydom like the DRA1 or something.  It depends on the power going to the pump and how you're going to break it or if it has a control line disable input or what exactly.