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Before a moisture meter is purchased it has to be checked what you want to measure. Is it humidity (air moisture) or moisture (material moisture)?
After that question is answered our moisture meters split in two categories:
- humidity meter
- moisture meter
Humidity meters are used to measure the humidity in the environment. Humidity meters for this application are available in different constructions and designs depending of the field of use. There are humidity meters with memory like our PCE-313A or the PCE-HT 110. Also handheld devise without memory like our PCE-555 are available. For accurate use in the research field or for calibration our PCE-330 is used.
Beyond this some devices have the ability to attach more sensors or they come direct as a pyrometer.
Furthermore to our handheld devices for temporary use you can find moisture meters or moisture sensors for steady use. These sensors forward the result via BUS or standard electrical signal to a data logger or process control system. Moisture sensors with this construction are often mounted on a wall. The target of these sensors is it to check the climate conditions in a warehouse for example.
For numerous moisture meters different filters for the protection of the sensor are available. For example we have a sinter filter what lets the humidity passes through, but it does not let any water through so the lifetime of the sensor is longer. Although we have a PTFE filter what protects the sensor from chemical contamination. For industry use we have a moisture sensors for custom application available that comes with heated sensor elements, which protects the sensor in a high humidity area, what makes them suitable for this.
Moisture meters for abs. moisture
Moisture meters for abs. moisture respectively material moisture for materials distinguish from a humidity meter that the moisture meter is calibrated (or adjusted) to a certain material.
That means that the user has the ability to measure the moisture of a certain material precise.
Moisture sensors for material moisture differ in the measurement principle and because of that also in the field of use.
A very common measurement method is the resistance method. This measuring method works destructive. In the field it means that, for example, two nails are inserted in the material and between the two needles the electrical resistance is measured. In the device itself the result will be converted through a conversion chart to the real moisture content and it will be displayed in %.
Another measuring method, in the field of handheld moisture meters, is the capacitive measuring method. This method is nondestructive. The moisture sensor creates an electric field via two contacts and measures the capacity. As more moisture is present the higher is the capacity. The moisture meter will give a result direct in %.
The above descript measuring methods are used in the field of construction moisture measurement with moisture meters.
If you want to measure the moisture of bulk material, like plastic granulate or food, the above measuring methods cannot be used. For this you can get moisture meters, with a long sword, where a sensor for rel. humidity is attached to. Through internal calibration characteristic curves the meter calculates the rel. humidity into material moisture. This measurement is preformed through the equilibrium moisture content (EMC).
The monitoring of the rel. humidity while stocking goods is very important. Some goods and products are only allowed to be stocked when a certain environmental condition is given. A humidity meter helps warehousemen and quality assurance representatives to store the goods safely and in line with the relevant regulations. This humidity meter can be a handheld or precise stationary device. A humidity meter that needs to be installed in the warehouse has to be placed at a certain point. The displayed result of the humidity meter can be shown on different ways:
- Displays the humidity on a small panel display in the control room or on site
- Displays the rel. humidity on a large display
- Placing of the measured value in the intranet of the company
Furthermore the measured values can be stored. Especially for companies, where the environmental conditions must be recorded, an installed moisture meter with data logger is important. Such a moisture meter gives the user next to the visualization of the values the ability for a complete documentation of the conditions in the warehouse. The measurements can be transferred into Excel, csv, etc. after they have been saved.
All moisture meters come factory calibrated. But as a moisture sensor tend to drift with time, they should be re-calibrated continuous, to measure the exact moisture content. You can re-calibrate the moisture meter with the optional calibration tools and standards or send the moisture meter to us or a calibration laboratory for ISO calibration.
In the following, you can see a picture of a PCE humidity meter in use. The picture on the right shows one of the humidity meters during long-time recording of the climate in a warehouse (moisture meter sensor attached to a rack).
Information on relative humidity: The relative humidity (RH) indicates the relation between the absolute (real) moisture and the saturation amount. The relative air humidity is measured with a humidity meter which is equipped with a display that shows values, for example, between 0 % (absolutely dry air) and 100 % (completely saturated air like fog, clouds or air in a vapour bath). This measurement does not apply to all humidity meters. In some cases, the measurement range is restricted. The physiological comfort zone ranges from 40... 65% rh.
As warm air takes on more water vapour than cold air, humans tend to perceive the air as dry in the winter and as sultry in summer. If the air is warm, the amount of water vapour it would contain if it was saturated is increased. This decreases the percentage of relative humidity, even if the real amount of water remains constant. Similarly, cooler air decreases the amount of water vapour which increases the percentage of RH. Condensate generates if there is excess water in saturated ambient air. Some of our humidity meters can also calculate the dew point or dew point temperature in addition to measuring the relative humidity and temperature.
The dew point temperature is defined as the temperature at which the current water vapour content in the air is the maximum (100 %) relative air humidity. Thus, the dew point temperature is a parameter that does not depend on the current temperature. One possibility to measure the dew point temperature is cooling down metal until the surface is covered with water vapour. The temperature of the metal at that time represents the dew point temperature. As mentioned before, many of our humidity meters show the dew point directly on the display.
Compressed air systems have been used in a wide range of technology fields including welding, heat treatment, cutting, forging, and transportation. Continuous monitoring of the systems condition allows for correct operation within production processes or where it is necessary to automate equipment and machinery. During the preparation process, large volumes of atmospheric air are introduced into the filtration system, filtering out various harmful particles including oil, moisture, combustion residue, and dust that are considered harmful to the pneumatic systems. However, the filter is designed with a minimum size limit allowing tiny particles such as moisture to pass through into the system. This convenient and user-friendly pneumatic system can become damaged should moisture begin to condense inside of the system.
As the temperature decreases, the amount of condensed moisture in the air begins to increase and over time may reach its saturated condition with a relative humidity of 100%, where the dew point has reached equal temperature. As the temperature increases, the opposite occurs. For this reason, systems may contain different values, as well as different amounts of condensation in the compressed air. A common factor among the different systems is the hindrance of moisture accumulation within a pneumatic system, as this is why all of the excessive moisture must be removed from the pneumatic system at different stages.
Varying amounts of moisture in the system can cause corrosion inside the pipe lines, contamination of the compressed air due to a mix of moisture and oil particles, excessive wear on the system components, and deterioration of final product quality. Because of this, it is absolutely prohibited in manufacturing involving foodstuffs, beverages, medical supplies, and electronic equipment, however, there are some instances within the industrial branches where permissible levels are allowed. Despite this fact, strict monitoring and compliance with the standards are required.
Moisture may be both, devastating and saving, depending on the amount of it present in the product and the distribution in the material. Moisture monitoring is one of the mandatory tasks, especially when it goes about storage and manufacturing. Raw materials as well as the finished products require strict and accurate moisture amount measurement. The question: how to perform the accurate measurement when it goes about bulk materials or liquid materials is a fair one, since application of the wrong measuring instrument may provide false results and thus, led to undesirable consequences, like too dry material output, loss of the required properties of the material (concrete), mold formation (grains and crops) etc. Inline moisture measurement has brought the process of moisture measurement to an absolutely new level, since it provided continuous moisture measurement at all stages, starting from the preparation up to the control of the finished product. It may be grain, sand, pellets, sawdust, different types of cereals, concrete, various suspensions and many other materials – the main point is that application of the moisture meter for inline measurement allows carrying out the accurate and repeatable measurements for each particular material. The first obvious problem when it goes about big amounts of the product – in the hopper, silos, on the conveyor belt, in the concrete mixer – the moisture distribution maybe not homogeneous. That is why surface measurement is not working and all the devices that may provide only surface measurement or the measurement of a very thin layer will be not right.
The moisture meters designed for inline measurements may have different optical design, and each particular measuring task determines the choice of the measuring device: convenience of mounting, the highest measurement efficiency for the material, measuring method. The microwave method is one of the most popular for the measurement of moisture content in the bulk materials, when the material is not evenly distributed, when the moisture accumulation is not the same or the density of the material is quite high. The challenging tasks like those are not a problem for the meters operating on the microwave measuring principle. Due to the option of the preliminary calibration of the device for each particular material, the average moisture content can be measured accurately. The inline moisture meter copes with the temperature compensation, or the possible difference in the moisture content at different parts of the batch, uneven density etc. Since moisture measurement has the task of determination the part of water in the total material or product and correspondingly, the deviation from the norm and permissible moisture content, the dielcometric method of measurement has become a very appropriate measuring principle for the most challenging measuring tasks. The value of dielectric permittivity of the materials is different from that of water. The signal penetrates into the material and due to the software that goes together with the device, the value for the moisture content is calculated for the whole amount of the material, which is important, not sample or just one part of the whole. The advantage of such moisture sensors is that the length of the probe is not equal to the depth they measure. The changes in the electromagnetic wave (its refractive index) in the material are registered and measured by the moisture meter, thus the dielectric properties of the material under control are analyzed. The operator may rely on the device, since the calculation is carried out due to the software and calibration tables that are stored in the device.
The application areas of inline moisture meters are numerous. The modern devices have been brought to a revolutionary new level and due to the application of the special materials for the electronic units, some models are suitable for application even in the explosive surroundings and at very high temperatures. The manufacturing processes should not be stopped for the measurements, the only condition – is the choice of the correct design and appropriate mounting of the device. Starting from the agricultural sector, where the measurement of various crops and grains are essential, moving further to the manufacturing of the construction materials – like concrete, clay, sand, crushed stone etc., and finishing with the heavy industry, like mining or oil refining or petrochemical, when it goes about coal, ores, oil or fuels – in all the spheres the application of the moisture measuring equipment is indispensable.
The advantages of introduction of highly developed technical equipment, such as moisture meters, are evident: significant improvement of the efficiency of the working process and performance, facilitation of the moisture measurement and no need of bringing the machines to the standstill for the measurements, measurements in the total material on site, without collecting samples for the laboratory, high accuracy and reliability, opportunity of quality control of the raw material, easy control of the final product.