Preamp for USB-6366?

[GS]

We'd like to add a gain of 10 preamp to 3 channels of a USB-6366. Is there anything available for doing this?

George

[WilliamEarle]

Hi George,

Each AI channel of the USB-6366 has a PGIA (Programmable Gain Instrument Amplifier) driving each ADC. The possible gains of the amplifier result in the following voltage ranges:

10V to -10V

5V to -5V

2V to -2V

1V to -1V

If you select the 1V to -1V range, the PGIA is effectively a x10 gain amplifier of the input signal to the analog-to-digital converter. However, the DAQmx API specifies things in terms of voltage ranges instead of gains. This is to make the voltage values you can read for each gain a little more clear.

DAQmx will also handle scaling voltage values for you; for example, if you provide a 1V input signal and select any of the above ranges, the DAQmx read method will return 1V even though the hardware is using a different gain on the PGIA for each range.

The DAQmx Create Channel (AI Voltage) API method has a "minimum value" and "maximum value" parameter. To get the gain you want, set these values to -1 and 1, respectively. This setting will apply to all channels.

To apply the value to individual channels, you can set the DAQmx Channel property "Active Channels" to the channels you want to change the voltage range for, and then set the "Analog Input: Maximum Value" and "Analog Input: Minimum Value" property.

William Earle

National Instruments R & D | Software Engineer | DAQ Software

[GS]

Yep, I was aware of all of that. We need an extra gain of 10. I thought maybe NI had a preamp to tack on the front end.

George

[WilliamEarle]

Hi George,

The standard way to get a lot of gain for DAQ devices is using SCXI. Unfortunately, the USB-6366 is a screw-terminal device and does not have a way to cable to SCXI, so it is not supported for the device.

With the USB-6366, you will have to create external circuitry to get the gain you desire. What are you trying to measure, how many channels do you need, what sample rates do you need, and do you need simultaneous sampling? If you are open to using other hardware, we have several products with the voltage range you are looking for that will not require any external circuitry.

William Earle

National Instruments R & D | Software Engineer | DAQ Software

[GS]

We need three channels with at least 1.5 M samples/sec for each. So I think we do need the simultaneous sampling.

[WilliamEarle]

Do you need to use USB? And what accuracy do you need (i.e. smallest step in voltage you need to be able to detect)?

If you need USB, the 6366 is the only DAQ device that will be able to go 1.5MS/S/ch, but there are other options for other buses.

William Earle

National Instruments R & D | Software Engineer | DAQ Software

[WilliamEarle]

Do you need to use USB? And what accuracy do you need (i.e. smallest step in voltage you need to be able to detect)?

If you need USB, the 6366 is the only DAQ device that will be able to go 1.5MS/S/ch, but there are other options for other buses.

William Earle

National Instruments R & D | Software Engineer | DAQ Software

[WilliamEarle]

If you need USB, the 6366 is the only DAQ device that will be able to go 1.5MS/S/ch, but there are other options for other buses.

[GS]

We currently have 16 bits at +/- .1V which is about 3uV per lsb.  We are trying to maintain that level which is about 10% on a 30uV signal which is the smallest signal we are trying to receive.

It doesn't have to be USB, but I don't think we want to have to get a PXI chassis for this one application.

George

[WilliamEarle]

All of our 16-bit simultaneous sampling devices that can go at 1.5MS/s/ch or faster are either USB or PXIe based. So, it looks like the USB-6366 with external circuitry will best match your requirements.

William Earle

National Instruments R & D | Software Engineer | DAQ Software

[WilliamEarle]

All of our 16-bit simultaneous sampling devices that can go at 1.5MS/s/ch or faster are either USB or PXIe based. So, it looks like the USB-6366 with external circuitry will best match your requirements.

William Earle

National Instruments R & D | Software Engineer | DAQ Software

[WilliamEarle]

All of our 16-bit simultaneous sampling devices that can go at 1.5MS/s/ch or faster are either USB or PXIe based. So, it looks like the USB-6366 with external circuitry will best match your requirements.

[WilliamEarle]

William Earle

National Instruments R & D | Software Engineer | DAQ Software