Analog Input – Smacq

Analog Input is the process of quantifying continuous varying signals, converting analog signals into digital data using an Analog-to-Digital Converter (ADC), and uploading this data to a computer. This functionality is widely used in Data Acquisition Devices (DAQ). When considering relevant parameters for analog inputs in a DAQ system, the main focus lies on the number of channels, sampling rate, resolution, and range.

Number of Channels

The number of channels for analog inputs refers to the number of channels available for analog signal acquisition. In devices capable of configuring both single-ended and differential input modes, the number of channels can be divided into single-ended input channels and differential input channels, with the latter usually being half of the former. In single-ended input，all input signals share a common ground reference. This method is suitable for scenarios where the input signal voltage is relatively high, the wire length from the signal source to the analog input hardware is short, and all input signals share a common ground reference. If the signals do not meet these standards, differential input should be used. With differential input，each input signal has its own ground reference, reducing noise errors as common-mode noise can be eliminated through the wires.

Sampling Rate

5kSa/s Sampling Rate

10kSa/s Sampling Rate

20kSa/s Sampling Rate

50kSa/s Sampling Rate

Simultaneous Sampling：refers to a DAQ system where each analog channel has its dedicated ADC, ensuring that all channels are sampled strictly simultaneously without any time difference. Asynchronous Sampling：on the other hand, typically utilizes multiplexing techniques, where a single ADC measures multiple signals. After capturing one channel, the ADC switches to another channel and continues the process repeatedly. As a result, the effective sampling rate for each channel and the number of channels sampled are inversely proportional, with a time gap of 1 sampling interval between two adjacent channels. For instance, a 1MSa/s asynchronous DAQ system with 8 channels will have a maximum sampling rate of 125kSa/s per channel, with a 1μs time gap between adjacent channels.

Resolution

The resolution of an analog-to-digital converter is defined as the number of bits used to represent the analog signal. The higher the resolution, the more segments into which the signal range is divided, thereby enabling detection of smaller voltage changes.

Take a 16-bit analog input as an example, when operating within a ±5V range, the distinguishable voltage will be: (5 * 2) / 65536 (2^16) = 15.27 μV.

The following set of graphs shows the time-domain waveform of a sine wave sampled with different resolutions in the range of 0 to 1.

2-bit Resolution

3-bit Resolution

Range

The range represents the minimum and maximum voltage values that the analog-to-digital converter can quantify. Many versatile data acquisition devices by Smacq allow users to select different ranges, even setting different ranges for different channels. This flexibility allows users to match the signal range to the ADC’s input range, fully utilizing the measurement resolution.