Difference between static and dynamic DACs

[ssomnath]

Hi, I am trying to understand the difference between a static and a dynamic DAC. I am going to be working on a project that has a very high IO count of 30 analog outputs. I need a 16 bit resolution board. I intend to update the outputs at a low frequency in the order of 1 Hz (on user deand). I was suggested to use the NI PXI 6704 board with 32 outputs. In order to future proof our equipment, we are planning on buying some board(s) that are capable of fast output update rates (few hundred Hz). I want to know what I am losing and gaining with static and dynamic DACs. What boards (that are reasonably fast) would work best for such high IO count? I am looking at the 6733 but I am not convinced entirely that this is the best alternative. 

[kellis.wiseman]

Hey Suhas,

The main difference between the two DACs is static is software timed while dynamic is hardware timed. As for the card, it really depends on how fast you need to generate samples. You will probably need a dynamic card to achieve an output rate higher than 1kHz. You might take a look at the cDAQ9264- it has 16 inputs (you could use two cards in a cDAQ 9174 chassis for 32 inputs). You could also buy a PCI-6723 which has 800 kS/s per channel for one channel and 45 kS/s per channel for 32 channel. If you need any other suggestions, just post back! Hope this helps. 

~kgarrett

[ssomnath]

Thanks for getting back,

The DACs form 1/2 of my hardware requiremets. I need to acquire data for 30 channels at a very fast rate for which I have been limited to the PXIe 6368 boards. I need a PXI compatible DAC solution. The only boards that I can find are all limited to 4 output channels with FPGA boards which are unnecessary for my work. Could you please suggest the best possible DAC boards within the PXI form factor (I will be using a PXI chassis) keeping in mind that I need 30 channels as a minimum. 

I am also considering the viability of using a multiplexer for my solution if the DACs have small channel counts. Considering that I need to output up to +- 10V as a minimum, would a combination of multiplexers and DACs work for me?

[Jackie_B]

Hey Suhas, 

There are a lot of approaches we could take to find a solution that best fits your needs. Just to clarify what you are looking for, I'd like to ask a couple more questions. When you collect these 30 anolog signals, how will you be manipulating them before outputting them? You stated that you are limited to PXIe 6368 boards. How many will you be using and what PXI chassis do you have? You stated that you were going to acquire the signals at a very fast rate, but update the outputs at a very slow rate. Why is this?

Regarding the multiplexer, I would like to have a better understanding of your set-up before I advise you regarding this. 

To summarize and clarify, your specifications are: 

30 I/O analog channels

16 bit resolution board

Is this correct? Are there any other specifications?

Thank you and I look forward to your response!

Jackie

Applications Engineer

National Instruments

[ssomnath]

I am sorry for the confusion. I meant to say that I am limited to the PXI form factor because the only ADC boards that I can use are the PXIe 6368s. I'd have to use two of those boards to meet the 30 inputs requirements. However, this also satisfies the 8/30 outputs. I was thinking of using three PXI 6733 to make up for the remaining 22 outputs. It is sufficiently accurate - 16 bits, pretty decent response / settling time, etc, doesn't have any unnecessary things like FPGAs, etc.

I plan to acquire the inputs. Perform simple algebraic manipulations, nothing taxing, to find and apply the appropriate output. I am still planning my PXI system so I can go for a larger chassis if required. I feel that the outputs are limited ot slow rates because I can acquire data much fast at the rate of 2MS/sec/ch while the ouputs are generally in the order of 1MS/sec/8 channels. In that regard i feel that the DAC boards would probably be the bottleneck in terms of theoretical execution time.

I did look into some multiplexing boards, nothing really caught my eye as they all had time scales for switching and settling in the range of a few m-secs.

In summary, I need to be capable of outputting 30 outputs (-10 to +10 V minimum) with 16 bit accuracy with settling, response times in the microsecond ranges.

Thanks,

Suhas 

[Eric_L]

Hello,

There are alternatives for the acquisition of 30 analog inputs besides a pair of PXIe 6368. They are as follows:

PCI-6259

PCIe-6259,6363,6353

PXI-6254,6259

PXIe-6363,6259

All of these cards are capable of 32 analog inputs at 16bit with a sample rate of 1MHz. It is also important to consider the measurement type (single ended or differential), some of these cards support only single ended or half the number of channels as a differential measurement.

As far as the output side is concerned you can use either PCI-6733 or PXI-6733

If you use a MXI controller in with an external computer to control the cards in the PXIe chassis, you can use the PCI/PCIe cards in the computer along with the PXI/PXIe modules. If you wish to use an embedded controller in the PXIe chassis, you will have to get all PXI/PXIe modules.

Eric L

[ssomnath]

To keep my equipment future-proof, would it be wise to buy everything that is PXI and not PCI, so that I won't have to worry about adding a controller to the PXI chassis in place of the MXI card?

[Eric_L · Accepted solution]

Hi,

If you get all PXI/PXIe modules, you will either have to buy a MXI controller to connect it to the desktop or spend more money and get an embedded controller for the PXIe chassis. If you wish to run real time applications in the future, you may want to spend more money upfront and get the embedded controller instead of the MXI connection. The MXI connection allows more system flexiblity than the embedded controller because it allows you to run additional devices that may not be avaible in PXI form factor. Both methods are the same in terms of being future proof, they just offer different operating options (Flexibility or Real-Time).

Eric