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What is zero, positive and negative error in a screw gauge? Physics practical

ZERO ERRORS IN A SCREW GAUGE

1. 1. SCREW GAUGE -IMAGE
   2. NO ZERO ERROR
   3. NO ZERO ERROR- IMAGE
   4. POSITIVE ZERO ERROR
   5. POSITIVE ZERO ERROR -IMAGE
   6. NEGATIVE ZERO ERROR
   7. NEGATIVE ZERO ERROR- IMAGE
   8. « HOW TO DECREASE ERRORS IN SCREW GAUGE »?
   9. CONCLUSION

ZERO ERRORS IN A SCREW GAUGE

SCREW GAUGE- IMAGE

OBJECTS TO BE MEASURED WITH A SCREW GAUGE:

The first step in screw gauge is placing the object between the anvil and spindle.The types of objects commonly measured with a screw gauge include measuring the diameter of wires, rods or any cylindrical object with a small diameter, determining the thickness of thin sheets of foils of metal or other materials, and measuring diameter or thickness of small objects  like beads,screws or nuts.

 

Impact on errors:

Screw gauge is primarily designed for measuring objects with circular cross sections. Screw gauge is best suited for  measuring objects within a specific range size.Objects that are irregular in shapes or that have curved surfaces(not flat) can cause the anvil and spindle to not make proper contact. This may lead to a zero error, causing either a positive or negative discrepancy in the reading.

 

Plane Surface in a screw gauge:

The plane surface refers to the flat, smooth surface of the object being measured or the surface against which the screw gauge’s anvil and spindle make contact.This is especially  important for ensuring the accuracy of the measurement because non-parallel or uneven surfaces can lead to inaccurate readings.

The concept of zero error occurs when the instrument gives inaccurate readings when there is no object placed between the anvil and spindle (when the screw is closed).

 

Importance of plane surfaces:

Accurate measurements: Ensures precise contact with the object being measured.

Zero error determination : This can be done by bringing  the anvil and spindle into contact. If these two surfaces are not flat it can lead to incorrect zero error readings.

Consistent measurements: Consistent contact between the plane surfaces ensures repeatable measurements, reducing discrepancies between readings.

Plane surface: Ensure the surface of the object being measured flat and properly placed against the anvil for accurate readings.

 

Anvil and Spindle:

Anvil: The fixed stationary part of the screw gauge with a flat, smooth surface.

Spindle; The moving part of the screw gauge with a flat, smooth surface at its tip.

The anvil and the spindle are the two primary components that directly measure the object.When using a screw gauge, the spindle moves toward the anvil to compress the object being measured.The anvil is stationary, while the spindle moves.

Impact on errors:

For accurate measurements, the anvil and spindle should be perfectly parallel and aligned.Misalignment or wear on either the anvil and spindle can introduce a zero error.Additionally dirt or damage to these parts can cause inaccurate readings.  

Scale coincides:

The term scale coincides with the alignment of the main scale and the thimble scale in the screw gauge when the instrument is properly calibrated to zero.

If the zero marks perfectly overlap, it indicates that the screw gauge is calibrated correctly and there is no initial error. That is,when the thimble scale and main scale are perfectly aligned, the reading is accurate, with no error.

 

Thimble scale:

Thimble scale is the rotating component of the screw gauge,which is a crucial component of a screw gauge.Thimble scale measures the finer fraction of the measurement (typically in hundredths of a milliammeter.The main scale provides the larger measurement (in millimeter)  while the thimble scale adds the finer reading. 

The thimble scale is essential for precise measurements using a screw gauge.Understanding its role in identifying and correcting zero errors ensures accurate readings and reliable experimental results.

Error reading:

If the thimble scale is not calibrated correctly or if it does not coincide with the main scale when the instrument is zeroed, this results in either positive or negative error.

Scale reading:

The final measurement is obtained by combining the values from both the main scale and the thimble scale.The scale reading is the sum of these two values, giving the final measurement of the object.

Impact on errors: 

An incorrect scale reading can cause due to misalignment, a zero error, or a non-flat lane surface.To find the zero errors of any screw gauge, the thimble is turned with the aim that the spindle progresses toward the Anvil.

At first the screw of the Circular/Head scale is gone to connect with the Anvil, so the level completion (level finish) of the screw contacts the Anvil and further it is checked by turning the ratchet.

NO ZERO ERROR

On the off chance that the zero of the circular scale (Head scale) precisely matches (exactly coincides) with the zero of the pitch scale (main scale), then, at that point, the mechanical assembly is said to have no zero error.

NO ZERO ERROR- IMAGE

POSITIVE ZERO ERROR

In case zero of the Circular/Head scale is under the reference line then the zero error should be positive.

Exactly when the zero error is positive, the contrasting zero correction is negative and this value will be deducted from the measured value.

POSITIVE ZERO ERROR -IMAGE

For example, the second division of the Circular/Head scale concurs with the zero of the pitch/main scale. For this show circumstance the zero of the Circular/Head scale is under the reference line then the zero error should be positive that is +0.02 mm and the zero correction is negative that is – 0.02 mm which is to be deducted from the measured value.

ALITER:

The second division of the Circular/Head scale agrees with the zero of the main/pitch scale. Here the reference focuses are taken as (0, 100). The later division close to the 0 of the reference focuses.

How to correct it to zero? It is basically by removing 2 from the coincidence second division. Then the zero correction(adjustment) is negative and the zero error is positive.

Least count of the screw gauge is 0.01 mm, thus the zero correction and zero error are – 0.02 mm and +0.02 mm separately.

Exactly when the zero error is positive, the contrasting zero correction is negative and this value will be deducted from the measured value.

NEGATIVE ZERO ERROR

If zero of the Head/Circular scale is above the reference line then the error should be negative. Exactly when the error is negative, the looking at zero correction in the device is positive and this value will be added to the measured value.

NEGATIVE ZERO ERROR- IMAGE

For example, the 97th division of the Circular/Head scale corresponds with the zero of the pitch/main scale. For this show circumstance the zero of the head scale/circular scale is above the reference line then the zero error should be negative that is – 0.03 mm and the zero correction is positive that is + 0.03 mm which is to be added to the measured value.

 

ALITER:

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The 97th division of the Circular/Head scale corresponds with the zero of the main/pitch scale. Here the reference focuses are taken as (0, 100). The 97th division close to the 100 of the reference focus.

How to correct it to hundred? It is fundamentally by adding 3 from the incident 97th division. Then, at that point, the zero correction/adjustment is positive and the corresponding error is negative.

Least count of the screw gauge is 0.01 mm, so the zero correction and zero error are +0.03 mm and – 0.03 mm independently.

« HOW TO DECREASE ERRORS IN SCREW GAUGE »?

• • Select a screw gauge that is in good condition.

• • Make sure that the screw gauge is clean and free of dirt.

• • While taking the measurement, hold the screw gauge firmly and steadily.

• • Avoid using too much force while rotating the screw.

• • For correct measurement, take multiple readings and take average out of it.

CONCLUSION

Zero error of a screw gauge is a systematic error that can be positive, negative.The three different types are mentioned above.The screw gauge errors are mainly due to wear and tear of screw, anvil and other repeated usage of screw gauge parts.The zero error of the screw gauge can be corrected by subtracting the zero error from the measured value. Did you ever check these errors in your school physics laboratory?

 QUESTIONS

• • What is the source of error in screw gauge?

• • How do you know if a screw gauge is zero error?

• • Why do we use zero correction?                                                               

  •  NEET PHYSICS -RELATED LINKS

• NEET PHYSICS – Screw gauge practice questions
• Screw Gauge Numericals