Why does not work this PID regulation?

[rinpocse91]

HI

Its a simulated DAQmx, there is no real device. I dont understand what is the problem. The proces value never reach the setpoint.

[nathand]

How could it work? Are you expecting the simulator to simulate your unknown system, and you want the output that you write to the analog output to have an effect on the analog input measurement? How would the simulator know what effect it should have?

A simulated analog input channel always returns a sine wave. Writing a value to a simulated analog output does nothing, other than allowing you to verify that it doesn't generate an error.

[mikeporter]

What does the output of the pid do? That isn't shown anywhere.

Also there is a fundamental problem with using simulated DAQ in this way. There is no connection between the simulated output and the simulated input.

Mike...

[rinpocse91]

thanks i am new in this field and have to learn so much.

[rinpocse91]

Is there any option to solve it without real device?

[mikeporter]

What is your goal? Are you prototyping a real system or learning about pid control?

There are pid examples the ship with LabVIEW. You could put a shift register on the loop and then define a transfer function that converts a pid output into the input for the next iteration.

Mike...

[rinpocse91]

I d like to solve this regulation in LV, but there are other problems. Maybe not problems just i have no enough knowledge.

there is a proportional pressure relief with 0-10V input range. There is a load cell in the end of the cylinder"s rod.

The signal from the cell (mv) come to the daq and with pid, i d like to regulate the pressure relief . Its just a simulation but i did not find AIO bridge daq. The load cell has got a bridge, so i need a daq like NI 9237 except that 9237 has no got analog output, with i can control the pressure relief.

[Zody]

Hi,

Why do you need an analog output on 9237. As you are posting the pressure relief has an input range of 0-10V. For that you would need a Analog Output with that range.

Ex. NI 9263 http://sine.ni.com/nips/cds/view/p/lang/ro/nid/208806

Basically, your system will have two modules, one for reading data from the sensor and the other one for controlling the pressure relief.

If you want to learn more about PID and implementation in LabVIEW, I would suggest you to go through this manual:

 http://www.ni.com/pdf/manuals/372192d.pdf

Best regards,

IR

[rinpocse91]

Hi thank you, its an useful answer!

Yes, i have a pressure relief with 0-10V analog input and a load cell with 0-20mV/V output. I thought I can do this regulation with 1 device. But if i understand you, i need two device. A receiver and transmitter. So i need a NI 2937 which capable handle load cells bridge and an another daq to regulate the pressure relief.

Am I right?

Thanks!

[Zody]

HI rinpocse91,

Yes, I can confirm one more time that if you want to use NI 9237 to read the data from sensor (load cell) than you will need another C Series Module (NI 9263) for Analog Output.

Basically, NI 9237 is a recommended device to use for load measurement because it has all the signal conditioning necessary for bridge based sensor (bridge completion, voltage excitation, etc.)

Some of the bridge sensors (loadcells) have a device that can provide voltage excitation and converts the reply from the sensor in a 0-10 V signal.

If your sensor has such a device, than you might be able to use only one device for your project (a multifunctions DAQ) that has both Analog Input and Output. For example, you can use a NI USB 6341. But there are plenty of other types depending on your sampling rate and other technical specifications.

I would recommend you to contact your local NI representative and discuss details about your project and they will advise you what device is the best for your application.

Best regards,

IR