Do You Know Your Measuring Instruments? Quiz

Answer: Anemometer

An anemometer is a common instrument used in the meteorological department to measure wind speed. It is very difficult to measure the speed of wind as it cannot be seen. Indirect methods are used.

There are many designs for an anemometer. The basic principle is that hemispherical cups mounted horizontally catch the blowing wind and rotate the vertical cylindrical shaft holding them up, and the rotational speed of this shaft is calibrated to measure the wind speed.

With the advancement in technology, other indirect methods like measuring the change in temperatures, pressure, etc. are also used to measure wind speed.

Answer: Sphygmomanometer

'Sphygmomanometer' is a combination of the Greek word 'sphugmo' meaning 'relating to the pulse' and 'manometer' - a pressure measurement device.

A sphygmomanometer consists of a cuff and a dial. The doctor puts the cuff around the arm and applies pressure until blood flow is stopped in the target artery. The applied pressure is slowly released until blood flow just starts which the doctor can identify by use of a stethoscope. This pressure is the 'systolic' pressure. The applied pressure is further released until it has no effect on the blood flow. This pressure is the 'diastolic' pressure.

Both the systolic and diastolic pressure readings characterize the blood pressure. The ideal systolic reading is 120 and ideal diastolic reading is 80. Any values more than 20 above these are considered high blood pressure.

Answer: Thermometer

A thermometer measures temperature and is one of the most common measuring instruments found.

The thermometer works on the principle of thermal expansion - liquids expand on heating them. A thermometer consists of a thin tube with a working liquid. As the liquid is heated, it expands and the liquid level rises in the calibrated tube. The calibrations are usually made for two scales - the Celsius Scale and the Fahrenheit Scale.

The size of the thermometer depends on the working liquid used. Usually mercury is used as it has a low specific heat capacity and heats quickly. Sometimes water is used and a very large tube is required in this case.

37 degrees Celsius or 98.6 degrees Fahrenheit is the normal body temperature. If you are significantly above this (above 38.5 Celsius or 100 Fahrenheit) visit the doctor as you are running a fever.

Answer: Tachometer

A tachometer measures the rotating speed of any rotating shaft. Most tachometers used are of two types - mechanical and electrical.

A mechanical tachometer makes use of the centrifugal force produced by the rotating shaft which is directly proportional to the rotational speed of the shaft. This force is used to extend or compress a spring using a suitable linkage mechanism and a pointer connected to the spring displays the RPM reading on a scale.

An electrical tachometer makes use of magnets present on the rotating shaft which produce eddy currents inside a metallic speed cup whose rotation due to these eddy currents activate a spring mechanism which is connected to a pointer calibrated to display the RPM reading on a scale.

Answer: Pyranometer

A pyranometer measures the amount of sunlight received on a horizontal surface. Two arrangements can be used for the purposes. One arrangement makes use of a thermopile and another uses a solar cell called a photo diode.

In a thermopile pyranometer, sunlight is made to fall on a black carbon plate which gets heated up and is connected to an unexposed carbon plate together forming a thermocouple. Many such thermocouples suitably arranged form a thermopile which produces a voltage and generates electricity. The amount of electricity produced is calibrated to the amount of solar radiation received.

In a solar-cell type pyranometer, sunlight is made to fall on a light sensitive solar cell called a photo diode which is connected to an amplifier. The electricity generated by the system is used to calibrate the amount of solar radiation received.

Answer: Calorimeter

A calorimeter is an instrument used to measure the heat of chemical reactions or physical changes. It is the principal instrument of 'calorimetry' - the science of measurement of heat.

One of the main purposes of a calorimeter is to measure the heat capacity or the specific heat capacity of various objects. Heat capacity is the heat required to raise the temperature of the object by unit degree Celsius and the specific heat capacity is the heat capacity per unit mass. A common arrangement for measuring this is the bomb calorimeter.

The bomb calorimeter works on the principle: "Heat lost by a hot body equals the heat gained by a cold body".

Answer: Breathalyzer

A breathalyzer is a device used to estimate the blood alcohol content (BAC) to check if a person is drunk and driving. It is difficult and impractical to conduct field blood tests to determine this. Hence, the person's breath sample is used for the purpose of testing.

Alcohol, when ingested, gets absorbed in the GI tract. It gets into the blood stream and when blood goes to the lungs, the alcohol, being volatile, evaporates and comes back in the air flow and is breathed out. This breath of the allegedly drunk driver is passed through the breathalyzer unit containing a reagent which changes colour under the influence of alcohol and a photo cell system calibrated to the change in colour indicates by what degree the person is drunk or not drunk.

Answer: Barometer

Air pressure is a very important parameter to predict weather. A simple instrument that measures this is a barometer. Two common types of barometers are the Torricellian barometer and the aneroid barometer.

The Torricellian barometer consists of an inverted, evacuated, tube placed in a trough of mercury. Due to the air pressure, there is a rise of mercury inside the tube. This rise measured from the base of the mercury level indicates the pressure exerted by the atmosphere at that place. A rise of 76 centimeters or 760 millimeters of mercury is considered to be equivalent to one atmospheric pressure or 101325 pascals.

The aneroid barometer consists of an air-tight metallic box pressed against a spring. When pressure acts on the box, its surface displaces inwards and there is a compression of the spring whose displacement is calibrated to a dial which displays the pressure.

Pressure measurements are very important to meteorologists as they give information on the possibility of cyclonic storms or temperature rises.

Answer: Dolorimeter

Pain is probably the most difficult sensation to quantify.

An approach for measuring pain can only be found experimentally. Pressure, heat or electrical stimulation applied to determine what level of these applied physical quantities induces a sensation of pain was one way of "measuring" pain. All these methods come under the field of 'dolorimetry' or the measurement of pain sensitivity and all devices used are dolorimeters or 'pain-measuring instruments'.

A measure of pain is necessary while administering anesthesia to patients as an improper amount may have serious consequences. It is also used for diagnosis of injuries and testing of analgesics (pain-killers).

Pain scales may be both quantitative or qualitative. The person feeling the pain is asked to rate the pain based on a preset scale in a quantitative pain scale. A description of the pain serves as the qualitative pain scale. Both these are considered by the therapists while diagnosing the reason and the remedy for the pain.

Answer: Micrometer

A micrometer is a simple instrument used to measure very small lengths such as the diameter of a very thin wire. In a micrometer, the small axial movement equivalent to the distance to be measured is transformed into the rotation of a screw whose movement is calibrated to the length to be measured axially.

The two major factors contributing to the accuracy in measurement are the major diameter of the screw and the pitch or lead of the screw. The pitch of the screw is the distance between two successive screw threads measured at the same point. Both these factors amplify the axial length into the rotational movement.

Another common instrument to measure small distances is the Vernier Calipers but the micrometer is much more accurate and precise.