measurement of humidity

1. What is Psychrometer?
A psychrometer is a hygrometer made up of two thermometers that are
identical. One thermometer’s bulb is kept wet, causing it to record a lower
temperature than the dry-bulb thermometer due to evaporation cooling.
A psychrometer is a device for measuring air humidity. It does so by measuring
the temperature difference between a dry thermometer bulb and a wet
thermometer bulb that has lost some moisture due to evaporation.
A psychrometer tests both the dry and wet bulb temperatures at the same time.
A wet wick mounted over the thermometer bulb is used to determine the
temperature of the wet bulb. Practically any kind of thermometer can be used.
Sling Psychrometer
The relative humidity, which is calculated as a percentage, can be determined
using a sling psychrometer. It’s calculated by multiplying the amount of
moisture in the air at a given temperature by the maximum amount of moisture
the air could hold at the same temperature, dividing by 100, and multiplying the
quotient by 100.
A wet-bulb thermometer and a dry-bulb thermometer are kept in a sling
psychrometer. Using regular tables and maps, a sling psychrometer may be used
to calculate the physical and thermal properties of moist air. It’s usually used to
figure out relative humidity.

2. The wet bulb is covered in muslin, which is soaked in water and acts as a wick.
When the web bulb is removed from the bath, it cools due to evaporation. A
sling psychrometer is one that has the bulb whirled around to speed up
evaporation.
Design of Psychrometer
A wet-bulb thermometer and a dry-bulb thermometer are kept in a sling
psychrometer. Psychrometric charts are complicated graphs that show the dry-
bulb temperature, wet-bulb temperature, relative humidity, specific volume,
dew point temperature, humidity ratio, and enthalpy of moist air at a specific
atmospheric pressure.
A dry-bulb thermometer is a regular thermometer, while a wet-bulb
thermometer is one with a cloth-wrapped bulb that has been moistened with
distilled water. One bulb is dripping wet, while the other is completely dry. To
test the temperature, we expose the dry bulb to the cold. We wrap a cloth wick
around the wet-bulb and soak it in water until it’s ready to use.
Working of Psychrometer
The amount of evaporative cooling on the psychrometer’s wet bulb is
proportional to the amount of moisture in the air. Drier air absorbs more
moisture from the bulb, which causes it to cool down faster. The temperature
does not change as much because the warmer air cannot retain as much water
from the bulb. In other words, the more humid the air is, the greater the change
in the wet bulb temperature.
Much information about atmospheric conditions, such as humidity, air
temperature, surface temperature, and dew point, can be shown on a digital
screen at once. However, these devices must be calibrated to local conditions
for 20 to 30 minutes before use, and the wet bulb sensor will dry out if not used
for a prolonged period of time.

3. As a result, despite needing a little more legwork on the part of the user, the
good old manual psychrometer retains its appeal. They would use a
psychrometric chart to determine the final humidity reading after reading both
bulb temperatures.
Uses of Psychrometer
While psychrometers are no longer widely used, they are still sometimes used to
calibrate humidistats, which regulate the internal humidity of air conditioning
and heating systems in buildings. Psychrometers were once used in the
construction of building ventilation systems.
A psychrometer tests both the dry and wet bulb temperatures at the same time.
A wet wick mounted over the thermometer bulb is used to determine the
temperature of the wet bulb. Practically any kind of thermometer can be used.
In some ships, the primary wet bulb temperature measurement system is an
electric psychrometer. They use it as a backup for air temperature and dew point
sensors that are automatically mounted.
Psychrometers are used for musical instruments such as pianos, guitars, and
violins, which can be affected by excessive humidity. Paints are susceptible to
humidity, so it’s used in the coating’s industry.

4. Dynamometers
Introduction
This article takes an in depth look at dynamometers.
You will learn more about topics such as:
 What is a dynamometer
 How dynamometers are used
 Types of dynamometers
 Dynamometer test procedures

5. A dynamometer is a measuring device used to determine the torque, force,
speed, and power required to operate the drive on a machine or motor, which
can be measured by evaluating the torque and rotational speed of a motor
simultaneously. Beyond the common use of dynamometers, there are other uses
for them, such as tests of engine management controllers and the examination of
combustion.
When force is applied to a flexible metal ring on a dynamometer, it bends and
measures the applied force. The measurement of force using dynamometers is
an essential part of automobile production to determine horsepower, power
absorption, and rotary speed.
To maintain their instruments and ensure the accuracy of readings, users
regularly calibrate and test dynamometers.
How a Dynamometer Works
The best explanation of how a dynamometer works is to envision a spring in a
two part mounting. One end of the spring is anchored to a base with the other
end connected to the force to be measured. As the spring is stretched by the
force, a reading registers on a scale. This simplistic representation of a
dynamometer is very similar to a spring balance but provides readings in units
of force or Newtons (N).
Though this simple example can provide a reading, it does not have the strength
to measure the power of a 250 hp engine. A more sophisticated and technical
device is required for that type of job, which is much larger and resembles an
electric motor or gas engine.

6. A large dynamometer is a variable load that is attached to the drive of an engine
or motor. As the motor powers up, the dynamometer absorbs the power being
produced to provide data on the torque and power of the motor. As the power is
absorbed, the dynamometer dissipates the massive amount of power generated
through electromagnetism.
As can be expected in the modern era, the data produced by a dynamometer is
fed into a computer. There are several varieties of software available to collect
dynamometer readings. Though DOS tends to be going out of existence, a few
versions of DOS software are still being used. The most common type is
Windows based.
The readings from the software include:
 ambient temperature
 barometric pressure
 humidity
 oil and coolant temperature
 exhaust temperatures
 airflow
 exhaust oxygen
 throttle position
 engine rpm
 manifold pressure
 crankcase blowby
With the use of dynamometer software, it is possible to measure, record,
observe, and assess any kind of data from an engine. Most manufacturers and
producers use dynamometers for basic data readouts. Dynamometer producers
know that the more things you measure and quantify, the better will be the
quality of the final product. With every test being performed consistently since
any aspect of the process can create variations in the results. Compiling a wide
range of data can account for any possible fluctuations and variables.

7. What is Dew Point?
The Dew Point is the lowest temperature that allows water vapour to remain in a gas without
condensing to a liquid state. As the air or gas temperature drops, its ability to absorb water
vapour drops until it becomes completely saturated and below this dew point temperature,
water droplets will start to form.
In pressurised systems such as compressed air distribution networks, the dew point is directly
related to the temperature AND system pressure. As pressure increases, the dew point
temperature also rises meaning that the potential for vapour to condense out occurs at a
higher temperature. In practice this can mean that instead of the condensing temperature
being quite low, the dew point could be at or above ambient temperature.
Why do I need Dew Point Measurement?
Industrial compressed air and gas systems can suffer damage from water contamination
directly or through the water subsequently freezing and expanding. Having water vapour in
the air or gas can also affect process or product quality. Removing water contamination
through filters and drying systems is common practice but as the dew point (and potential for
damaging condensation) changes with pressure, the risk of damage will vary throughout a
plant.
ISO 8573-1 defines a range of purity classes for compressed air including water with the
measurement expressed in terms of pressure dew point. ISO 8573-3 is the section that defines
measurement methods for humidity and ISO 8573-9 for liquid water.
Measuring the dew point can be a simple process and should be continuously monitored
according to the plant risk analysis recommendations. This needs to occur at the drying plant
before the distribution network and also at critical points of use. By measuring the dew point,
efficient control of the drying/filtering system can be achieved to optimise the running costs
of the compressed air/gas system.
Particular emphasis should be placed on any part of the system where the pressure increases
or the ambient temperature decreases as these are the situations where problems can occur
quickly. For example, the air ring main leaves one building to go to another and the ambient
outside air is or can be significantly lower than the indoor ambient. Additional drying
capability may be needed and monitored in order to prevent condensation as the pipe leaves
the building.
Monitoring the dew point is a key indicator of system health that can be used to guide
maintenance tasks as well as maintain plant compliance with the purity classes set in ISO
8573-1.

8. Dew Point Sensors
S211 -60degC Dew Point Sensor
S212 -50degC Dew Point Sensor
S215 -20degC Dew Point Sensor

9. S220 -100degC Dew Point Sensor
S230 - S231 -100degC Dew Point Sensors

10. S305 Dew Point Monitor

11. S520 smart dew point meter
S201 Dew point sensor

12. COSA Xentaur Corporation
84 Horseblock Road Unit H
Yaphank, NY 11980
Tel: 631-345-3434
Email: sales@cosaxentaur.com
Hygrocontrol COSA Xentaur GmbH
Mosel Str. 2B
63452 Hanau, Germany
Tel: +49 1618192790
Email: info@hygrocontrol.de
I N N O VAT I V E M E A S U R E M E N T S O L U T I O N S
MOISTURE MEASUREMENT OF GASES
“Moisture and humidity are significant factors affecting us directly and indirectly through
their meteorological aspects, their contribution to the quality and cost of natural and
synthetic products, their influence on the chemical, electrical, physical and parasitic life
support characteristics of most manufactured and processed goods, their relationship
with storage life, energy cost and conservation, material degradation, etc.”
The amount of water vapor in air and many different gases is vital to a wide variety
ofindustrial processes--especially the manufacture of electronic components, and is
one of the variables in most fields of research which must be accurately measured and
controlled.
Until the age of modern electronics there was no alternative to the wet-and-dry
bulbhygrometer for measurement of relative humidity and this simple device remains as
one of the cheapest and most accurate forms of measurement. Making measurements
when the moisture content is drier than about 20% relative humidity is a very different
matter.
The development of the aluminum oxide sensor drastically changed the science of
moisture measurement. The invention of the capacitance sensor opened up such
possibilities that new applications for the technique were discovered almost on a daily
basis--indeed new applications are still being found for this highly versatile sensing
device forty years later.
The sensor is a variable capacitor with an ultra high purity aluminum core and porous
gold film outer electrode with a special dielectric layer between. It rapidly comes into
equilibrium with the surrounding atmosphere, and the capacitance of the sensor varies
in direct proportions to the water vapor content.
Cosa Sensors are manufactured in a variety of measuring ranges to meet the needs of
applications as varied as making sure that periscope prisms remain clear, medical gases
in hospitals are not contaminated, plastic bottles for carbonated drinks don’t burst, and
that the highly specified gases used in VLSI (very large scale integration) silicon chip
manufacture are within specification.
With such a large market it is natural that many other manufacturers have tried to
develop aluminum oxide sensors. However, none have come anywhere near the
performance of the Cosa product for these very good reasons:
1) Accuracy: Xentaur XTR-100 sensors are produced in a robotized manufacturing system
and vigorous QC procedures assure high uniformity. One curve correction function fits all
sensors, making sensors freely interchangeable.
2) Capacitance Change: The capacitance change of a XTR-100 sensor over the full
measuring range is about 60 times larger than that of a conventional Al2O3 sensor.
In addition, the capacitance change per 1°C change of dewpoint at the dry end is
approximately 500 times larger. The much larger signal change makes it easier to handle
the sensors signal electronically. The result is more stable and accurate readings, which
are less prone to other influences such as drift, temperature and electrical noise.
3) Automatic Calibration: Any measuring system needs to have its calibration checked
from time to time. With the Xentaur sensor it takes about one minute and needs no other
equipment or operator skill. The XTR-100 sensors flatten out at the top and saturate at
a predesigned level above +20°C. With other types the sensor (or even the complete
instrument) must be returned to the manufacturer, or the user has to buy extremely
expensive calibration equipment.

13. COSA Xentaur Corporation
84 Horseblock Road Unit H
Yaphank, NY 11980
Tel: 631-345-3434
Email: sales@cosaxentaur.com
Hygrocontrol COSA Xentaur GmbH
Mosel Str. 2B
63452 Hanau, Germany
Tel: +49 1618192790
Email: info@hygrocontrol.de
I N N O VAT I V E M E A S U R E M E N T S O L U T I O N S
4) Speed: The XTR-100 sensor responds significantly faster to a change in water vapor
content than conventional sensors. Xentaur sensors dry down from -40°C to -60°C in 90
seconds. In dry to wet change conditions response speed is virtually instantaneous.
5) Temperature Coefficient: Xentaur sensors have a small and uniform temperature
coefficient. Conventional sensors exhibit a substantial coefficient (i.e. readings vary
significantly with temperature changes). Some other manufacturers supply their sensors
in thermostatically controlled chambers in order to obtain a stable reading.
OTHER PRICIPLES OF OPERATION
The capacitance sensor is not, of course, the only way of measuring small amounts
of water vapor in air and other gases, but it is certainly the easiest, most reliable, and
usually the cheapest.
1) Chilled Mirror Instruments: Generally accepted as the standard to which other
instruments are measured against. This is a very simple instrument in principle, although
complicated and expensive in practice. The air or gas passes over a very small mirror on
which shines a light source. The mirror is chilled, usually by using a Peltier device, until
its temperature is below the sample dewpoint temperature. Condensation or frost forms
on the mirror, scattering the light beam and detection of the scattered light is used to
control the mirror temperature. Cosa offers the MBW line of chilled mirror hygrometers.
These analyzers are laboratory grade instruments, extremely accurate and very
expensive. Normally used as standards, these analyzers are not well suited to industrial
applications.
2) Electrolytical Instruments: These have a cell which is coated with Phosphorus
Pentoxide. The theory is that the sample gas passes through the cell at a closely
controlled flow rate and all the moisture is absorbed into the desiccant. Platinum wires
embedded in the desiccant carry a current which electrolyzes this water into hydrogen
and oxygen and Faraday’s law is used to convert the required current into a moisture
measurement. Fine so far--but did you spot the deliberate mistake? The desiccant
absorbs ALL the moisture: clearly impossible, and the reason for quite large errors when
measuring at 10 parts per million moisture content and drier. The other disadvantages
are the need to accurately control sample flow rate, the very limited cell life, and the
several days it takes to obtain stable readings from a new cell.
3) Oscillating Crystal Instruments: These are very high-tech devices which use a tuned
crystal coated with a hygroscopic polymer. The sample gas passes over the crystal, the
polymer absorbs the moisture and the resonant frequency between the two gases
is used to measure the sample moisture content. (In some versions two crystals are
used to give a differential measurement). Not only do these instruments assume near
total absorption of the sample’s moisture but they also rely on their own reference
gas having an absolutely constant known moisture content close to zero--both being
equally unlikely. These are impressive instruments--extremely expensive--but having
questionable reliability when measuring very dry samples.
The type of hygrometer chosen by the user to perform a particular process
measurement of control function depends to a great extent on the compatibility of
the moisture measurement technique of the hygrometer type with the process of
interest. Xentaur aluminum oxide sensor technology is certainly the easiest, most
reliable, and usually the least expensive method of measurement for the vast majority of
applications measuring moisture. Specify Cosa dewpoint sensors for all your hygrometer
requirements.