How do you select an appropriate measuring range for an instrument?

What are the factors required to consider in selecting an appropriate measuring range for an instrument?  

• Selecting the appropriate measuring range for an instrument is an essential and includes considering various factors to ensure accurate and reliable measurements. 
• It is essential to refer to the specific guidelines provided by the instrument’s manufacturer and consult      with experts in the field or the instrument supplier for further assistance in selecting the appropriate measuring range if necessary.
• Some general steps and considerations help us to determine the suitable measuring range for an instrument.

Defining the Expected Range of Measurements:

• Clearly defining the parameters required to measure. 
• Understand the physical quantity, and unit of measurement, and determine the expected range of values required to measure.
• Consider both the minimum and maximum values that the instrument is likely to encounter in your application.
• Consider the expected range of values for the parameter you are measuring. The measuring range should cover the full range of values that you anticipate encountering during normal operation. If the range is too narrow, you may miss important data points, and if it’s too wide, you might lose precision.

Identify Potential Variations:

• Consider the variability in the parameter you are measuring. 
• Identify the minimum and maximum values you expect the instrument to encounter during normal operation.

Consider Accuracy Requirements:

• Assess the required level of accuracy for your measurements. 
• Different instruments often have varying levels of accuracy at different points across their measuring range. 
• Choose a range where the instrument’s accuracy is acceptable for our requirement.
• Ensure that the selected range aligns with our accuracy requirement. Choose a range that matches the resolution and precision needed for your application.

Avoid Overloading:

• Ensure that the selected measuring range can handle the maximum expected value without overloading the instrument. 
• Overloading can lead to inaccurate measurements, damage to the instrument, or both.

Evaluate Potential Overloads:

• Check if there are any possibilities of exceeding the instrument’s measurement capacity. 
• Avoid selecting a range where measurements might exceed the instrument’s maximum capacity, as this can lead to inaccurate readings or damage to the instrument.

Consider Resolution, Precision, or Sensitivity:

• Evaluate or Take into account the required resolution precision or sensitivity of your measurements. 
• If you require high precision demand for some applications, choose a range of measurements that allows the instrument to provide the necessary level of detail in the measurements.

Future-Proofing:

• Consider potential changes in your application or environment. 
• If there’s a chance that the measurement range may change in the future, it may be wise to choose a more versatile instrument or one with a wider measuring range.
• This can save costs in the long run by avoiding the need for a replacement instrument.

Budget Constraints:

• Consider cost constraints and find a balance between cost and the required performance. Instruments with wider measuring ranges or higher accuracy tend to be more expensive. 
• It is the most essential factor to be considered in balancing the requirements within our capital investment.

Review or Consult Instrument Specifications:

• Refer to the technical specification of an instrument provided by the instrument manufacturer. 
• These specifications often include details about the instrument’s measuring parameters such as range, accuracy, resolution, and other parameters that might be relevant to your application.

Manufacturer Recommendations: 

• Consult the manufacturer’s guidelines and recommendations for the instrument. 
• Manufacturers often provide information on the optimal measuring range based on the instrument’s design and capabilities.

Select Multiple Instruments if Necessary:

• In some cases, it might be more practical to use multiple instruments with different measuring ranges rather than trying to cover a wide range with a single instrument. 
• This approach can provide more accurate measurements in specific sub-ranges.

Test and Calibration:

Once the instrument is in use, regularly calibrate and test it to ensure it continues to provide accurate measurements within the selected range.

Factor in Environmental Conditions:

Consider the environmental conditions in which the instrument will be used. Some instruments may have specific operating ranges regarding temperature, humidity, or other environmental factors.

Safety Margins: 

• Incorporate safety margins into your selection to account for unexpected variations or spikes in the measured parameter. 
• This helps to prevent instrument damage and ensures reliable operation even in challenging conditions.

General Characteristics for Selection of Measuring Instruments

Various specific terms define the characteristics and quality of measuring instruments as shown below

Accuracy:  The term accuracy is termed as the degree of agreement of the measured dimension with its true or actual magnitude.

Amplification: It is the ratio of the output value of the measuring instrument to the input value. It is known as magnification.

Calibration and maintenance: The calibration of an instrument is defined as the process of adjustment or setting of a measuring instrument with a defined set of values to issue process values that are accurate within a reference standard. Evaluate the calibration and maintenance needs of the instruments. Instruments with simple calibration procedures and lower maintenance requirements may be preferable for certain applications.

Drift or Stability: It is defined as the capacity of an instrument to maintain its calibration over time.

Linearity: It is defined as the accuracy of an instrument reading over its maximum working range.

Magnification: The ratio of measuring instrument output to the input dimension. It is also known as amplification.

Precision: it is the degree of an instrument to which a measuring instrument produces a repeated measurement of the same standard.

Repeat Accuracy: It is the same as accuracy, but repeated many times.

Resolution: The smallest dimensional value that can be visualized on a measuring instrument.

Rule of 10: A measuring instrument or gauge must be ten times more accurate than the dimensional tolerances of the part being measured.

It is also known as gage maker’s rule

A factor of 4 is termed the mil-standard rule.

Sensitivity: Smallest variation in a dimension that an instrument can distinguish or detect.

The speed of response: it is defined as the rapidity of a measuring instrument particularly when some parts are measured in rapid succession.

Stability: The stability of an instrument is defined as the capacity to maintain its calibration over time. It is      also known as drift.

Compatibility: Ensure that the selected instruments are compatible with the existing infrastructure and systems in your application.

Documentation and Support: Choose instruments from reputable manufacturers that provide thorough documentation, user support, and warranty services.

What are the factors considered for selecting measuring instrument?

The selection of an appropriate measuring instrument for a particular application also depends on the following factors.

1. Accuracy of the instrument.
2. Time required to obtain an output 
3. Equipment cost.
4. Operator skills
5. Environmental parameters such as temperature, humidity, dust, pressure, and so on
6. Size and type of parts to be measured.
7. Instrument zero error.
8. Physical quality of the material.

 Frequently Asked Questions

What is an appropriate measuring instrument for measurement?

Appropriate measuring instrument for measurement includes 

Rulers, Vernier callipers, micrometre screw gauges, measuring tape, and odometers.

Which instrument is considered as most precise tool for measuring length?

The Vernier calliper is the most precise tool used to measure the length & diameter of a pipe.

What is the measuring range of an instrument?

• Range of measured values for a measurand.
• It is established by a lower and an upper measuring range.

What is the most appropriate unit to measure distance?

Meters 

Why do we choose standard units of measurement?

Standard units are used in measurement for higher accuracy. 

What are the Range, Resolution, and Accuracy of measurement?

• Range: Range is the amount or a value that can be determined by the instrument.
• Resolution is the number of significant digits (to which a value is being reliably measured. 
• Accuracy:  The term accuracy is termed as the degree of agreement of the measured dimension with its true or actual magnitude.