Measurement Specialties USB-1616HS-2 Example Analog and digital scanning, once per scan mode

USB-1616HS-2 User's Guide Functional Details

If you want 256 oversamples, then each analog channel in the scan group will take 256 µs, and the returned 16- bit value represents an average of 256 consecutive 1 µs samples of that channel. The acquisition is triggered and 16-bit values—each representing an average of 256—stream to the PC via the USB cable. Since two of the channels in the scan group are temperature channels, you need the acquisition engine to read a cold-junction- compensation (CJC) temperature every scan.

Figure 8. Analog channel scanning of voltage and temperature inputs example

Since the targeted number of oversamples is 256 in this example, each analog channel in the scan group requires 256 microseconds to return one 16-bit value. The oversampling is also done for CJC temperature measurement channels, making the minimum scan period for this example 7 x 256 µs, or 1792 µs. The maximum scan frequency is the inverse of this number, 558 Hz.

For accurate measurements, you must associate TC and CJC channels properly

The TC channels must immediately follow their associated CJC channels in the channel array. For accurate TC readings, associate CJC0 with TC0, CJC1 with TC1 and TC2, CJC2 with TC3, CJC3 with TC4, CJC4 with TC5 and TC6, and CJC5 with TC7.

When the AI-EXP48 module is connected to the USB-1616HS-2, associate CJC6 with TC8 through TC11, CJC7 with TC12 through TC15, CJC8 with TC16 through TC19, CJC9 with TC20 through TC23, CJC10 with TC24 through TC27, and CJC11 with TC28 through TC31.

Example: Analog and digital scanning, once per scan mode

The scan is programmed pre-acquisition and is made up of six analog channels (Ch0, Ch2, Ch5, Ch11, Ch13, Ch15) and four digital channels (16-bits of digital IO, three counter inputs.) Each of the analog channels can have a different gain.

The acquisition is triggered and the samples stream to the PC via the USB cable. Each analog channel requires one microsecond of scan time. Therefore, the scan period can be no shorter than 6 µs for this example. All of the digital channels are sampled at the start of scan and do not require additional scanning bandwidth as long as there is at least one analog channel in the scan group. The scan period can be made much longer than 6 µs, up to 1 second. The maximum scan frequency is one divided by 6 µs or 166,666 Hz.

Figure 9. Analog and digital scanning, once per scan mode example

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