Using cDAQ9188 for acquisition and control of HVAC project

[alexander.bui]

Hello all,

I am in charge of a daq/control project and I need some help. My specific application is to run an experiment where I can continuously measure pressure and temperature in a test environment.  In addition, I will controlling some HVAC actuators (that are connected to duct dampers) and a supply fan VFD.  From test to test, I would be tweaking both of these controls to get to desired settings and then leaving them be.  Finally, I'll be controlling the open/close of solenoid valves according to a set schedule. 

So, all in all, I am tasked with:

(a) Data acquisition of pressure sensors, output signal 4-20mA
(b) Data acquistion of temperature sensors, output signal 0-10VDC
(c) Data acquisition of actuators feedback signal, output signal 2-10 VDC

(d) Control of damper actuators, input signal 2-10VDC

(e) Control of fan's variable frequency drive (VFD), input signal would be 0-10VDC
(f) Control of solenoid valves, open/close input signal would be 24VDC

(g) Data acquistion of VFD, output signal 4-20mA  (to display the fan speed)

My plan is to use the cDAQ9188 with the following modules to address the corresponding tasks listed above:

(a&g) NI9208, analog input +/- 21.5 mA

(b&c) NI9205, analog input +/- 10V

(d&e) NI9264, analog output +/- 10V

(f) NI9476, digital output 6-36V source

My questions are:

• Firstly, I'm wondering if my current setup addresses my needs.
• Can I generate signals for the actuators and supply VFD on the same module, despite their differences in supply voltage (24VDC and 480VAC respectively)?
• Likewise, can I acquire signals for the temperature sensors and the actuator feedback on the same module?
• Can all of my input signals be acquired simultaneously?
• Since cDAQ9188 has only three timing engine tasks, can I group a voltage analog input and a current analog input as one task?

I have not purchased any equipment yet, but I hope to soon once I get this information squared away.  Sorry for the long description, just want to make sure I cover everything.  Any help would be very much appreciated, thanks in advance.

Alex

Relevant documentation:

Pressure: http://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Transmitters/Series616W/Specs

Temp: http://www.dwyer-inst.com/Product/Humidity/HumidityTransmitters/SeriesRHP/Specs

Actuator: http://energycontrol.com/belimo_lf24-sr-s.aspx

VFD: http://www.danfoss.com/NR/rdonlyres/D1185810-9D78-4F6F-A257-F502E7F43F5C/0/HVACDriveGeneralSpecifica...

[Matt_L]

Hi Alex,

I can give a few pointers on this:

• It almost does, there are a few concerns I have here.
• I think you should be able to, but be careful with connections esp. with that 480VAC, make sure to isolate grounds and consider placing fuses between the 480 and wherever you're going with it.
• Yes, the 9205 should be able to do this.
• However, you won't be able to do simultaneous inputs with this chassis. 
• Yes, you'll have to use the same task for a few of the inputs.

[alexander.bui]

Hi Matt,

Thanks for the response. 

I will be sure to isolate grounds and consider fuses.  I have designed for a power disconnect between the 480VAC source and my equipment.

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• However, you won't be able to do simultaneous inputs with this chassis. 

---

Did you happen to mean simultaneous outputs?  If so, is there any cDAQ chassis that can perform simultaneous outputs AND inputs?  My idea of simultaneous might also be incorrect.  I consider a chassis to be capable of simultaneous IO if multiple modules can carry out their IO at the same time.  Would this thinking be correct? 

In my daq plan, I would do the following:

1. AI of pressure sensors
2. AI of temperature sensors
3. AI of actuators feedback signal
4. AI of VFD output signal, (to display the fan speed)

Question 1: I would like to accomplish all of these analog inputs by sampling each sensor once every 5 seconds.  I understand the modules have much higher sample rates (250kS/s, 500S/s etc...), but I would just like to confirm that I can sample from all these devices at the same time at a 1 Sample / 5 second rate. 

In my control plan, I would do the following, also simultaneously with the data acquisition.

1. AO to damper actuators
2. AO to fan's variable frequency drive (VFD)
3. DO to solenoid valves

Question 2: I would just like to confirm that I can do control the above devices....all at the same time with some output rate. 

Question 3: I have seen some applications that control a solenoid valve using a relay module, such as a NI9481, instead of a digital output module such as NI9476, for controlling solenoid valves.  If I am just focusing on controlling the open and close of a DC solenoid valve, would you recommend one approach over another? 

Thanks. These forums have been a big help.

Alex

[Matt_L]

Alex,

The simultaneous input I was referring to was for reading analog input signals simultaneously.  Some cards have an ADC for each input while others have only one ADC and a multiplexer, so it will switch between reading inputs and there will be some delay if your program is set to read these inputs all at once.  You should be able to perform input and output at the same time on the cards you've been looking at.

So for your first question, you should be fine as far as every 5 seconds goes, those sampling rates are more than enough.  But bear in mind that unless the module has simultaneous analog input, you will not be able to read 1 sample at precisely the same time on all inputs, there will be a small delay. 

Simultaneous output, you should be good there as well, for the analog side most devices will have a DAC for each output, and this should work simultaneously with the digital output.

As far as the solenoids go, I'm not too sure myself unfortunately, but there are a couple of forum posts here and here that look like they have some good suggestions, I would give those a look.

Glad to be of help!