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daq-and-datalogging:documents:accuracy-precision-resolution-and-sensitivity [2023/06/14 06:36] – created Scandiwebdaq-and-datalogging:documents:accuracy-precision-resolution-and-sensitivity [2023/07/27 21:39] (current) – Arthur Brown
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-====== TechTip: ======+====== TechTip: Accuracy, Precision, Resolution, and Sensitivity ======
  
-===== Accuracy, Precision, Resolution, and Sensitivity =====+**Objective**
  
-**Objective**\\  
 This document explains the difference between the terms accuracy, precision, resolution, and sensitivity as applied to a measurement system. This document explains the difference between the terms accuracy, precision, resolution, and sensitivity as applied to a measurement system.
  
-**Intended Audience\\  +**Intended Audience** 
-**This document is intended for users who operate and interpret the results of a DAQ measurement system.+ 
 +This document is intended for users who operate and interpret the results of a DAQ measurement system. 
 + 
 +**Overview**
  
-**Overview**\\  
 Instrument manufacturers usually supply specifications for their equipment that define its accuracy, precision, resolution and sensitivity. Unfortunately, not all of these specifications are uniform from one to another or expressed in the same terms. Moreover, even when they are given, do you know how they apply to your system and to the variables you are measuring? Some specifications are given as worst-case values, while others take into consideration your actual measurements.\\  Instrument manufacturers usually supply specifications for their equipment that define its accuracy, precision, resolution and sensitivity. Unfortunately, not all of these specifications are uniform from one to another or expressed in the same terms. Moreover, even when they are given, do you know how they apply to your system and to the variables you are measuring? Some specifications are given as worst-case values, while others take into consideration your actual measurements.\\ 
  
-**Accuracy**\\ +**Accuracy** 
 Accuracy can be defined as the amount of uncertainty in a measurement with respect to an absolute standard. Accuracy specifications usually contain the effect of errors due to gain and offset parameters. Offset errors can be given as a unit of measurement such as volts or ohms and are independent of the magnitude of the input signal being measured. An example might be given as ±1.0 millivolt (mV) offset error, regardless of the range or gain settings. In contrast, gain errors do depend on the magnitude of the input signal and are expressed as a percentage of the reading, such as ±0.1%. Total accuracy is therefore equal to the sum of the two: ±(0.1% of input +1.0 mV). An example of this is illustrated in Table 1.\\  Accuracy can be defined as the amount of uncertainty in a measurement with respect to an absolute standard. Accuracy specifications usually contain the effect of errors due to gain and offset parameters. Offset errors can be given as a unit of measurement such as volts or ohms and are independent of the magnitude of the input signal being measured. An example might be given as ±1.0 millivolt (mV) offset error, regardless of the range or gain settings. In contrast, gain errors do depend on the magnitude of the input signal and are expressed as a percentage of the reading, such as ±0.1%. Total accuracy is therefore equal to the sum of the two: ±(0.1% of input +1.0 mV). An example of this is illustrated in Table 1.\\ 
  
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 | 10 V | 9.989 V to 10.011 V (±11 mV) | | 10 V | 9.989 V to 10.011 V (±11 mV) |
  
-**Precision**\\ +**Precision** 
 Precision describes the reproducibility of the measurement. For example, measure a steady state signal many times. In this case if the values are close together then it has a high degree of precision or repeatability. The values do not have to be the true values just grouped together. Take the average of the measurements and the difference is between it and the true value is accuracy.\\  Precision describes the reproducibility of the measurement. For example, measure a steady state signal many times. In this case if the values are close together then it has a high degree of precision or repeatability. The values do not have to be the true values just grouped together. Take the average of the measurements and the difference is between it and the true value is accuracy.\\ 
  
-**Resolution**\\ +**Resolution** 
 Resolution can be expressed in two ways:\\  Resolution can be expressed in two ways:\\ 
  
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 A technique called averaging can improve the resolution, but it sacrifices speed. Averaging reduces the noise by the square root of the number of samples, therefore it requires multiple readings to be added together and then divided by the total number of samples. For example, in a system with three bits of noise, 23 = 8 , that is, eight counts of noise averaging 64 samples would reduce the noise contribution to one count, √64 = 8: 8÷8 = 1. However, this technique cannot reduce the affects of non-linearity, and the noise must have a Gaussian distribution. A technique called averaging can improve the resolution, but it sacrifices speed. Averaging reduces the noise by the square root of the number of samples, therefore it requires multiple readings to be added together and then divided by the total number of samples. For example, in a system with three bits of noise, 23 = 8 , that is, eight counts of noise averaging 64 samples would reduce the noise contribution to one count, √64 = 8: 8÷8 = 1. However, this technique cannot reduce the affects of non-linearity, and the noise must have a Gaussian distribution.
  
-**Sensitivity**\\ +**Sensitivity** 
 Sensitivity is an absolute quantity, the smallest absolute amount of change that can be detected by a measurement. Consider a measurement device that has a ±1.0 volt input range and ±4 counts of noise, if the A/D converter resolution is 212 the peak-to-peak sensitivity will be ±4 counts × (2 ÷ 4096) or ±1.9 mV p-p. This will dictate how the sensor responds. For example, take a sensor that is rated for 1000 units with an output voltage of 0-1 volts (V). This means that at 1 volt the equivalent measurement is 1000 units or 1 mV equals one unit. However the sensitivity is 1.9 mV p-p so it will take two units before the input detects a change. Sensitivity is an absolute quantity, the smallest absolute amount of change that can be detected by a measurement. Consider a measurement device that has a ±1.0 volt input range and ±4 counts of noise, if the A/D converter resolution is 212 the peak-to-peak sensitivity will be ±4 counts × (2 ÷ 4096) or ±1.9 mV p-p. This will dictate how the sensor responds. For example, take a sensor that is rated for 1000 units with an output voltage of 0-1 volts (V). This means that at 1 volt the equivalent measurement is 1000 units or 1 mV equals one unit. However the sensitivity is 1.9 mV p-p so it will take two units before the input detects a change.
  
-**The Measurement Computing USB-1608G Series Example**\\ +**The Measurement Computing USB-1608G Series Example** 
 Let’s use the USB-1608G DAQ device and determine its resolution, accuracy, and sensitivity. (Refer to Table 2 and Table 3, below, for its specifications.) Consider a sensor that outputs a signal between 0 and 3 volts and is connected to the USB-1608G analog input. We will determine the accuracy at two conditions: Condition No. 1 when the sensor output is 200 mV, and Condition No. 2 when the sensor output is 3.0 volts.\\  Let’s use the USB-1608G DAQ device and determine its resolution, accuracy, and sensitivity. (Refer to Table 2 and Table 3, below, for its specifications.) Consider a sensor that outputs a signal between 0 and 3 volts and is connected to the USB-1608G analog input. We will determine the accuracy at two conditions: Condition No. 1 when the sensor output is 200 mV, and Condition No. 2 when the sensor output is 3.0 volts.\\ 
  
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 **Summary Analysis:** **Summary Analysis:**
 +
 **Accuracy: Consider Condition No. 1.** The total accuracy is 369 µV ÷ 2 V × 100 = 0.0184% **Accuracy: Consider Condition No. 1.** The total accuracy is 369 µV ÷ 2 V × 100 = 0.0184%
  
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 |  ±1 V  |  9  |  1.36  | |  ±1 V  |  9  |  1.36  |
  
 +**More Information**
  
-More Information\\  +Please reach out to our support team on the Digilent Forum if you have any questions: [[https://forum.digilent.com/]]
-Please contact Measurement Computing Corporation if you have any questions or if you would like any further information.\\  +
- +
-Knowledgebase: [[https://kb.mccdaq.com/Default.aspx | kb.mccdaq.com]]\\  +
-Phone: 508-946-5100\\  +
-Fax: 508-946-9500\\ +
      
-Additional TechTips are available on our [[https://www.mccdaq.com/Technical-Articles | Data Acquisition Technical Articles web page.]]+Additional TechTips are available here in Digilent Reference: [[start]]