Measurement-computing USB-231 Manual do Utilizador descarregar pdf (Página 10)

Chapter 3

Functional Details

Analog input acquisition modes

The USB-231 can acquire analog input data in two different modes – software paced and hardware paced.

Software paced mode

You can acquire one analog sample at a time in software paced mode. You initiate the A/D conversion with a

software command. The analog value is converted to digital and returned to the computer. You can repeat this

procedure until you have the total number of samples that you want.

The maximum throughput sample rate in software paced mode is system-dependent.

Hardware paced mode

You can acquire data from up to eight channels in hardware paced mode. The analog data is continuously

acquired and converted to digital values until you stop the scan. Data is transferred in blocks of samples from

the device to the memory buffer on your computer. The block size varies depending on the sample rate.

The maximum continuous scan rate is an aggregate rate. The total acquisition rate for all channels cannot

exceed 50 kS/s. The following table lists the scan rate when scanning from one to eight channels.

Maximum continuous scan rate

# channels

scanned

Sample rate

(kS/s)

1 50

2 25

3 16.67

4 12.5

5 10

6 8.33

7 7.14

8 6.25

You can start a hardware paced continuous scan with either a software command or with an external hardware

trigger event.

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