Support for hardware triggering or rearm DAQmx device

[cpede]

I'm looking for a DAQmx supported device that supports the following application.

I want to acquire 1000 samples at 20 MHz whenever an external digital trigger is set.

The time between each acquisition is less that 1ms so I would prefer an automatic

rearm of the digital trigger so that it is ready for the next trigger pulse.

I also want to read out the 1000 samples.

Do you have a DAQmx supported device that supports automatic rearm of the trigger

so that I don't need to call Start and Clear Task between the measurements?

I'm using C++ so please provide answer using the API functions, and not VI's.

-cpede

[LucaP.]

Hi cpede,

As far as I know there is no DAQmx supported device which can acquire data at 20 MHz. The PCI/PXI-6115 is the fastest with 10 MS/s.

I don't see how many channels you need to acquire, but if it's <=2 then I recommend you to use a High Speed Digitizer with multiple record support. The rearm time depends on several factors, but is usually around 100 u.

What is multiple record support?

From the NI-Scope help.

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NI 5105/5114/5122/5124/5142/5152/5153/5154/5622 Multiple-Record Acquisition var L_helpType = "STD_ENG"; Dim hasPlayer, playerversion hasPlayer = false playerversion = 10 Do While playerversion > 0 On Error Resume Next hasPlayer = (IsObject(CreateObject("ShockwaveFlash.ShockwaveFlash." & playerversion))) If hasPlayer = true Then Exit Do playerversion = playerversion - 1 Loop is_FlashVersion = playerversion is_Flash = hasPlayer

NI 5105/5114/5122/5124/5142/5152/5153/5154/5622 digitizers support multiple-record acquisitions, which allow the capture of multiple triggered waveforms without software intervention. In this mode, the digitizer automatically begins a new acquisition in a new memory record immediately after finishing the previous one. Multiple-record acquisitions can quickly acquire numerous triggered waveforms because they allow hardware rearming of the digitizer. Between each record, however, there is a dead time during which no triggers are accepted. During this time, the memory controller sets up for the next record. There is also a holdoff between the last trigger in a record and the trigger of a new record. This means that the actual time between triggers is the greater of the between-record dead time plus pretrigger sample time and the holdoff time. There may also be additional dead time while the minimum number of pretrigger samples are being acquired. To increase the minimum time between triggers, use the trigger holdoff feature.

The number of records that can be acquired varies depending on the memory option of the device. NI-SCOPE currently has a limit of 100,000 records that can be acquired without fetching.

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What is the Trigger Hold-Off feature of the High-Speed Digitizers?

Important: NI digitizers are programmed with the NI-Scope driver!