For ADC’s that perform one sample per conversion the throughput rate is also referred to as the sampling rate – this is the case for Fusion. Sampling Rate or frequency is the rate at which the ADC acquires or samples the analog input and converts it to digital data. It is specified as samples per second ( S/s ) or Hertz ( Hz ).
The sampling rate is typically the inverse of the ADC Conversion Time. For example, an ADC that takes 10 microseconds to acquire and convert an analog signal to a digital value will be able to generate about 100,000 samples per second. In the case where only a single channel is being sampled, the channel’s sampling rate is equal to the total system sampling rate.
However, in the case where the sampling sequence contains multiple channels and where a channel may be sampled multiple times in relation to another channel, the sampling rate computation becomes more involved.
The following sections describe the sampling rate computation for SmartGen. SmartGen enables you to specify the minimum sampling time and minimum sampling rate. SmartGen then reports the total system sampling rate and the actual sampling rate of each channel.
General Formula for Sampling Rate
The general formula for sampling rate is as follows:
Total Sampling Rate = Total # of Samples / Total Conversion Time of all Samples
Channel Sampling Rate =
( (Total Conversion Time of all Samples for Channel) /
(Total Conversion Time of all Samples) ) *
(Total Sampling Rate)
The method for arriving at this formula is explained in the examples below.
Example: Equal Weight and Equal Conversion Time
All Channels have a conversion time of 2 ms, as shown in the figure below.
Equal Weight and Equal Conversion Time
In this case we have 10 samples which take a total
of 20 ms.
Thus, our total system sampling rate is: 10 / 20 ms
= 500 kS / s
Channel1 Sampling Rate: 4 ms / 20 ms = .20 * 500 kS /s = 100 kS /s
Channel2 Sampling Rate: 4 ms / 20 ms = .20 * 500 kS /s = 100 kS /s
Channel3 Sampling Rate: 4 ms / 20 ms = .20 * 500 kS /s = 100 kS /s
Channel4 Sampling Rate: 4 ms / 20 ms = .20 * 500 kS /s = 100 kS /s
Channel5 Sampling Rate: 4 ms / 20 ms = .20 * 500 kS /s = 100 kS /s
Example: Unequal Weight and Equal Conversion Time
In this example, the channels are not equally weighted in the sampling sequence,as shown in the figure below.
Unequal Weight and Equal Conversion Time
In this case we have 10 samples that take a total of 20 ms, giving us a total system sampling rate of 500 kS/s (as above). However, the individual channel sampling rates are different.
Channel1 Sampling Rate: 10 ms / 20 ms = .5 * 500 kS /s = 250 kS /s
Channel2 Sampling Rate: 2 ms / 20 ms = .1 * 500 kS /s = 50 kS /s
Channel3 Sampling Rate: 2 ms / 20 ms = .1 * 500 kS /s = 50 kS /s
Channel4 Sampling Rate: 2 ms / 20 ms = .1 * 500 kS /s = 50 kS /s
Channel5 Sampling Rate: 4 ms / 20 ms = .20 * 500 kS /s = 100 kS /s
Example: Unequal Weight and Unequal Conversion Time
In this example, channels have different conversion times and are not equally weighted in the sampling sequence, as shown in the figure below.
Unequal Weight and Unequal Conversion Time
In this case we have 12 samples in 20 ms, giving us a total system sampling rate of 600 kS/s.
Channel1 Sampling Rate: 7 ms / 20 ms = .35 * 600 kS /s = 210 kS /s
Channel2 Sampling Rate: 4 ms / 20 ms = .20 * 600 kS /s = 120 kS /s
Channel3 Sampling Rate: 2 ms / 20 ms = .1 * 600 kS /s = 60 kS /s
Channel4 Sampling Rate: 3 ms / 20 ms = .15 * 600 kS /s = 90 kS /s
Channel5 Sampling Rate: 4 ms / 20 ms = .20 * 600 kS /s = 120 kS /s