Generally, it must be ensured that the sensor of the thermometer has the medium flowing past it. This is generally achieved by having the thermowell or protection tube tip in the middle third of the pipeline. Why do modern protection tubes mainly have female threads for thermometer connections, and not male threads as in older specifications? The risk of damage with female threads is less than with male threads. Since the replacement of protection tubes is always fraught with difficulties.
Since it allows the thermometer to be removed without difficulty while the plant is running, this configuration is recommended. In the past, most thermometers were used with union nuts that fitted the male threads on the protection tube. What tests and inspections are stipulated for thermowells and protection tubes? In accordance with DIN Point 4. What tests are usual or possible for thermowells and protection tubes?
Common non-destructive tests are the pressure test and, for protection tubes and thermowells with a welding seam, the liquid penetrant test. In addition, to test the centrality of the bore, ultrasound or X-ray testing is possible.
To test the sealing, helium leak testing is an option. The surface finish or surface hardness may also be tested. This is used to refer to non-destructive inspections or tests on components in general. What is a hydrostatic pressure test? The hydrostatic pressure test is a pressure and strength test of the components of a thermowell or protection tube in accordance with the AD data sheet HP For the test, the thermowell or protection tube is clamped into a test fixture and loaded at room temperature with a defined test pressure and duration e.
In general, one differentiates between external and internal pressure testing. Typical test pressures are 1. The test is performed with water with a chloride content What is a helium leak test? The test is able to detect minimal leakage rates and is considered the most sensitive test method for leak testing.
In general, one should distinguish between an integral and local test method. In the integral test, leak rates e. After passing a helium leak test, the thermowell or protection tube is labelled with a corresponding sticker. What is a PMI test? The PMI positive material identification test proves which alloy constituents exist in the material.
There are various common test procedures. A characteristic feature of this procedure is the fire mark that is left on the workpiece.
What is a dye penetrant test? With the penetrant test in accordance with DIN EN , fine surface cracks and porosities in weld seams can be made visible. After cleaning the surface to be inspected, a contrast agent red or fluorescent is sprayed on. Through the capillary effect, this agent penetrates any surface defects there might be. After re-cleaning the surface, a developer white is then sprayed on, which extracts the contrast agent from any hairline cracks, etc.
After passing a liquid penetration test, the thermowell or protection tube is marked with "PT". What is a X-ray testing? Through an X-ray test to EN or ASME Section V, Article 2, Edition , for example, full penetration welds on thermowells can be investigated with respect to irregularities cracks, voids, insufficient bonding. Here, depending on the dimensions of the thermowell, up to five X-ray images may be necessary to determine irregularities with sizes What is an ultrasonic test? Through an ultrasonic test to DIN EN ISO , for example, full penetration welds on thermowells can be investigated with respect to irregularities cracks, voids, insufficient bonding.
To do this, the reflections of a radiated ultrasonic signal from the interfaces of irregularities are measured. To determine the position of the irregularities, the ultrasound machine is set in advance with the aid of a reference body. The ultrasonic method can also be used to measure the wall thickness of a thermowell, in order to determine the bore centrality. Why do some users specify a polished thermowell surface, and others define a high roughness or knurling of the area in the flow?
This depends on the usage of the thermowell. A polished surface has a higher corrosion resistance than a rough surface. The rough or knurled surface has an advantage with respect to the vibrational excitation by the Karman vortex street, meaning such thermowells can withstand higher flow rates than smooth thermowells.
Do thermowells or protection tubes need to be CE marked? Thermowells or protection tubes must not be CE marked, in principle. Are there any GOST certificates for thermowells and protection tubes?
GOST certificates only exist for measuring instruments and a thermowell and protection tube is only considered a component part of a thermometer. What is the maximum insertion length for a thermowell or protection tube? For protection tubes, the maximum length is limited by the manufactured lengths of the tubes, which is about meters. Thermowells are made of solid material and limited by the production length of the drill hole, which, for each product is between 1, mm and 2, mm.
Longer thermowells have to be made by welding individual elements together. What does calibration mean? To calibrate in measurement technology means to determine the deviations in the complete measuring instrument. With calibration there is no technical intervention at the measuring instrument, such as zero point adjustment, span and linearity setting, etc..
With indicating measuring instruments calibration establishes the measuring deviation between the display and what is claimed to be the correct value of the measurand. For material measurements, for example dimensions, the measuring deviation is determined by measuring the difference between the marking and the correct value.
For measuring chains one determines the deviation between the measured value of the output signal and the value that this signal should have with an ideal transfer characteristic and a given input value. What is adjustment? Adjustment means setting or alignment of a measuring instrument also a material measure so that the measuring deviations are made as small as possible or that the magnitudes of the measuring deviations do not exceed the error limits.
The adjustment, therefore, requires an intervention which, in most cases, permanently alters the measuring instrument or the material measure, e. What is verification? The verification of a measuring instrument also a material measure includes the testing, from the competent calibration authority in accordance with the calibration instructions to be carried out, and the stamping.
Through the testing it is determined whether the measuring instrument submitted meets the calibration specifications meaning whether it, in the nature of its properties and its metrological properties, satisfactorily meets the requirements , in particular, whether the magnitude of the measuring deviations does not exceed the error limits n.
Through the stamping, it is certified that the measuring instrument has satisfied these requirements at the time of the testing, and through its nature is expected, if handled in line with the codes of practice within the calibration interval, to remain within the specified tolerance range. Which instruments are subject to obligatory verification and which are excluded from this is regulated by law.
How frequently, or after what interval, is the recalibration of a pressure measuring instrument required? What is an axial gradient? What does radial gradient mean? What does stability mean? The temperature difference between the minimum and the maximum for fluctuating temperature, taken over 30 minutes. What is the difference between a dry well calibrator and a micro calibration bath? The reference, which the calibrator controls, is mounted directly into the metal block.
They work with precious-metal thermocouples as standards and control thermometers. In these cases, the measurement uncertainties are higher than in calibrators which use a resistance thermometer as a standard.
The working range of micro calibration baths is unlike the dry block calibrators strictly limited, due to the use of liquids usually silicone oil instead of inserts. In order to be able to calibrate using these liquids, they must be sufficiently viscous at ambient temperature.
They do have the advantage of homogeneous mixing of the liquid due to a magnetic stirrer at the bottom, meaning no axial nor radial gradients are observed. What is the minimum immersion depth with dry well calibrators?
The minimum immersion depth for dry well calibrators is 70mm. This is driven by the axial gradient, since warm air rises from the bottom up. Should this minimum immersion depth of 70mm not be reached, an external reference thermometer must be used for calibration. This is then placed on the same level as the object to be calibrated and the results are compared with each other. The other alternative is to use a micro calibration bath, since with the thorough mixing of the liquid, there is no requirement for a minimum immersion depth.
Rule of thumb for recommended immersion depth: 1. Diameter of the test item x 15 or 2. What material are the inserts for a dry well calibrator made from?
The material for the inserts depends on the temperature range of the dry well calibrator. The selected material should have a temperature range far remove from the melting point. How must the inserts be designed in order to get the best results? The inserts should be drilled in accordance with the diameter of the test items.
In general, the bore diameter, taking the thermal expansion of the test item into account, should be selected to be as small as possible. Air gap between the thermometer and the bore will act as resistances to heat transfer and will significantly affect the heat transfer through heat conduction. As a consequence, the test bore diameter should be a maximum of 0. When test units with a large internal volumes should be calibrated with it e. For pressure transmitters with a small channel bore volume, a shut-off valve is needed.
The volume change of the piston with a complete spindle hub is only 3. NS pressure gauge. When using the CPH series reference pressure transmitters and pressure transmitters on the test item side, a shut-off valve is required. For which pressure and temperature ranges have the calibration laboratories been accredited? What is the German physical and technical test institute PTB?
The PTB, Braunschweig and Berlin, is the metrological state institute and Germany's highest technical body for metrology. It stores and develops the national standards for implementing the SI units and ensures their comparability on an international level by cooperation with other state institutes.
This includes, in particular, the propagation of the units of measure within the meaning of measurement technology traceability. For the propagation of the units, the PTB primarily operates accredited laboratories. To promote uniformity in metrology, and with the aim of an extended professional support, on the 3rd May, , a committee was established with the PTB for the development of measurement technology bases for calibration, in which the PTB and accredited calibration laboratories cooperate closely.
How do you recognise an accredited body? All bodies accredited by the DAkkS can prove their status by an accreditation certificate. In sovereign territory, the certificate is provided with the federal eagle. Moreover, the bodies can signal their accredited status by using the DAkkS accreditation symbols on test reports and certificates and thus document the high quality of their evaluation service.
The symbol consists of the protected DAkkS logo and a unique registration numbere. On its website, the DAkkS makes available a database of all accredited bodies www.
What advantages are offered by accreditations? For the company, accreditations promote international comparability and recognition of certificates and test reports. This transparency makes it easier for companies to gain access to national and international markets. Moreover, proof of accreditation is often the prerequisite of certain norms of "potential customers". The business relationship is only made possible by virtue of accreditation.
The consumer can rely on the data on the calibration certificate. Moreover, he knows that, depending on the data given, standards, regulations and international recommendations are thereby guaranteed conformity statement. Why should equipment be calibrated? To ensure consistent quality of the manufactured products, quality management according to the family of standards DIN EN ISO has been in force for years and is indispensable for many companies.
This standard requires that all quality-relevant features of a product must be tested and, when doing so, retraceable inspection equipment is regularly used.
Calibration ensures that the measured results are internationally comparable and product liability risks are minimised - an important prerequisite for competitiveness on tomorrow's markets.
What is an accreditation? Confidence in calibration stands or falls on the competence of those who deliver the assessment service. Many of these conformity assessment bodies substantiate the quality of their own work through an accreditation. In this process, they demonstrate to an independent accreditation body that they complete their activities competently, in compliance with legal and normative requirements and to an internationally comparable level.
In Germany, only DAkkS acts as a national accreditation body. What is a standard? Standard VIM : "Material measure, measuring instrument, reference material or measuring device intended to define, materialise, conserve or reproduce a unit or one or several values of a quantity. What is a national standard? A standard approved by national decision as basis for the determination of values of all other standards of the quantity in question SI unit.
What is a reference standard? A standard, in general of the highest available accuracy at a given place or at an organisation which can be used to carry out measurements there. What is a working standard? A standard routinely used for calibrating or testing material measures, measuring instruments or reference materials.
Calibration baths of such a volume always require the use of an external reference. The display is no longer reliable, owing to the volume and the gradient. For these reasons, no certificate will be issued for these baths. What is self-optimisation or autotuning? The PID terms for temperature control vary in value and combination, depending on the characteristics of the controlled system. In current use, there are a number of traditional methods proposed and implemented for determining the PID terms from the waveform of the temperatures to be controlled by the temperature controller.
This enables self-optimisation e. Among the self-optimisation processes are step response, limit sensitivity and limit cycle processes. What is the set point? The set point is the parameter that the temperature controller should react to. The time required to achieve stable control varies for each controlled system.
What are fluctuations and overshoots? Two-point control often involves undulation. A temperature rise above the set point, after the start of the temperature control, is referred to as overshoot. Temperature changes around the set point are referred to as fluctuations. A better quality of control is expected when the level of overshoot and fluctuation is low. What is the hysteresis? Two-point control switches the output on or off depending on the deviation form the set point.
This means that the output can frequently change with the smallest temperature changes. This can shorten the service life of the output relay and it can have a negative effect on the service life of the power switch. This difference between the switching points is known as the hysteresis. What is the derivative time? The derivative time is the time required when controlling a differential until a ramp deviation corresponds with the control output in proportional control.
The longer the derivative time, the stronger is the derivative component of the output signal. What is the integral time? The integral time is the defined time in which the integrator must reach the value of the step response of the P-controller.
The shorter the integral time, the stronger the effect of the integral component. If the integral time is too short, however, this can lead to fluctuations. What is a two-point controller? A two-point controller is a controller that works discontinuously, with two output states. Depending on whether the actual value is above or below the set point, the upper or lower output state is active.
Two-point controllers are used when the actuating variable is not a continuous variable, rather it can switch between two states, e. Though the two-point controller achieves a steady state, it never stops working.
With strong changes in the set point it can certainly control quicker than is possible with other control processes. What is P-control? P-control proportional control is used to hold an output in proportion to the deviation between the set point and the actual value.
What is D-control? D-function or derivative control function is used in order to hold an output in proportion to a time derivative function of the input. What is a PID controller?
PID control is a combination of proportional, integral and derivative control. Thus, through proportional control, the temperature is controlled smoothly without fluctuations. Through integral control, automatic offset-matching is made and through derivative control, a fast reaction to external disturbances is possible. What is fuzzy logic? Fuzzy logic is a theory which has been developed mainly for the modelling of uncertainties and vagaries from non-standard specifications.
It is a generalisation of two-valued Boolean logic. With this acquisition the product range in the field of calibration technology with the measurement parameter temperature offered by WIKA has been extended. In order to integrate the products into the WIKA websites, the previous model designations have been changed. Regarding their technical features the products remain unchanged. What are the benefits of optoelectronic switches in level measurement? How does a built-in magnetic system work?
A float with a built-in magnetic system moves with the level of the medium to be measured on a guide tube which has one or more reed switch contacts built into it. The magnet actuates the contacts at the pre-set switching heights and thus allows individual levels to be monitored.
The simple and tried-and-trusted principle of operation is suitable for a very wide range of applications. How does a level sensor work? These level sensors work on the float principle with magnetic transmission. The float's magnetic system actuates a resistance measuring chain that corresponds to a 3-wire potentiometer circuit in the guide tube. What is a magnetostrictive level sensor used for? These level sensors are used as measured value pick-ups for the continuous recording of levels, and are based on determining the position of a magnetic float according to the magnetostrictive principle.
What is a bypass level indicator? In a communicating bypass chamber mounted to the side of a vessel a float moves with the level of the medium to be measured. The magnetic field of the radial-symmetric positioned in the float at submersion height activates the magnetic roller display attached to the outside of the bypass chamber as well as the switching and measuring elements. What are the benefits of level sensors? What are the benefits of high-precision level measurement?
The simple and effective principle of operation is suitable for a very wide range of applications. In which areas can transparent sight glass level indicators be used? They are the most suitable gauges for steam application above 35 bar, where mica shields have to be used to protect the sight glasses from corrosion by the steam boiler water. They can also be utilised in a great number of other applications,in particular for observing interface layers or liquid colour.
A backlight illuminator can be fitted to the rear to improve visibility. How does a reflex sight glass level indicator work? The principle of the reflex level indicator is based on the reflection of light. In the gas or steam phase, the light is reflected by the prismatic grooves of the sight glass so that bright indication is achieved.
In the liquid phase, the light is absorbed, resulting in a dark indication of the level. What are the benefits of sight glasses in level measurement? Detection of liquid level with glass level gauges is almost independent from physical properties like refraction index, density, conductivity, colour Direct visualisation of the medium No power supply required Specified in accordance with several standards and customer standards Simple and well-known technology Robust design Extremely low certification efforts.
How low is the temperature of the medium which is stored inside the cryogenic vessel when it reaches the pressure gauge? A Cryo gas is a gas which is gaseous at ambient temperature and pressure and becomes liquid because of cooling and compression. Typical liquid gases which are stored in closed vessels are nitrogen, oxygen, argon, carbon dioxide, liquefied natural gas LNG and nitrous oxide.
If the temperature of the liquid gas inside the vessel increases, then the pressure inside the vessel increases as well. A vessel for liquid gases always consists of two vessels: one inner vessel and one outer vessel. There is a vacuum between the vessels which are connected by steel rods. The vacuum isolates the inner vessel from the outside temperature to ensure that the temperature of the medium inside the vessel is less influenced by the ambient temperature.
There are two pipes which connect the inner vessel with the pressure gauge mounted outside the vessel. One connects the upper part of the vessel gaseous phase with the pressure gauge and the other connects the lower part of the vessel liquid phase with the pressure gauge.
As soon as the gas in the pipe leaves the outer vessel, that is the isolated area, it will become gaseous. Within the pipe, the medium will reach the ambient temperature before it reaches the gauge.
As a consequence, the lowest medium temperature in the pipe outside the vessel is the ambient temperature. The medium is always gaseous when it reaches the pressure gauge. This memory chip stores the coefficients of the calibrated sensor and a complete history of the probe. This history includes the maximum and minimum value that the sensor has been exposed to and also the calibration dates.
What is the Kn factor? The nominal effective area of each piston-cylinder size is such that, under standard conditions, a piston loaded with 1 kg of mass will generate a pressure equivalent to the Kn value. All mass values, including the mass of the piston and of themass loading bell are adjusted to be a whole number or a fraction of a kilogram.
The nominal pressure defined for a pressure balance is calculated as Kn multiplied by the mass loaded in kg. Corrections are applied to Kn to calculate the pressure defined within the accuracy tolerance of the piston-cylinder assembly used. The use of Kn and whole-number masses in no way affects the traditional pressure equation nor the factors that affect a pressure measurement made with a pressure balance.
It is intended to be a tool that reduces operator confusion and errors by simplifying the calculation of mass loads and measured pressures. For which electrical measurement parameters have the calibration laboratories been accredited?
For which pressure ranges has the mobile calibration service been accredited? On-site calibration: Gauge pressure: -1 bar … 8, bar Absolute pressure: 0 bar … 8, bar Calibration vans: Gauge pressure: -1 bar … 4, bar Absolute pressure: 0 bar … 60 bar.
Can a 3. The statement that a 3. On cost grounds, this is only used in a reduced form in many cases. Who is Mensor and what do they do? Mensor was founded in in Houston, Texas, and has been dedicated to the design and manufacture of the finest high-accuracy measurement, calibration and control instruments and test systems for pressure available.
In , Mensor relocated to San Marcos, Texas. From the first Mensor quartz manometer produced for the aviation industry in to the advanced computer-controlled pressure calibration systems of today, Mensor's name has become synonymous with reliability and innovation in the field of precision pressure measurement, control and calibration.
Do gas-actuated thermometers fall within the Pressure Equipment Directive and may an appropriate CE marking be applied?
The products should not be marked with CE or their conformity confirmed in respect of the above-mentioned directive. A manufacturer's declaration can be requested if required. How is a calibration interval determined? To ensure that correct measurements can be carried out permanently, the inspection equipment used must be monitored or calibrated at regular intervals.
This period of time corresponds to the calibration interval. The user of a calibration item has sole responsibility for defining the exact calibration interval.
There are, however, many different factors that effect the determination of the calibration interval. They include, for example, the required measurement uncertainties, defintion of standards and directives, operating conditions of the inspection equipment, frequency of use, subsequent costs caused by measurements using a defective instrument and the manufacturer's recommendation.
What is an air data test set? An air data test set is a an electronic controller which, based on a supply pressure, automatically provides a pressure at a variable and adjustable rate. Air data test sets are specifically developed to convert the pressure to be controlled into a height or rate of climb and velocity.
As a result of the high accuracy, control stability and ability to simulate altitude and velocity, an air data test set is particularly suitable as a reference for aircraft workshops and also for instrument manufacturers and calibration laboratories in the aviation industry, in order to make calibrations on sensors and displays.
The tests for this report were performed in a water channel. The same design rules are also in use to design helical strakes in air, for example on industrial chimneys in accordance with DIN EN Is an initial verification possible for mechanical thermometers? Since 01 January , the new Measurement and Verification Act has been in force. This no longer permits any initial verification for dial thermometers. If an initial verification is required to place the measuring instrument on the market for the first time, this requirement will be met through a conformity assessment procedure.
The conformity assessment of a measuring instrument basically replaces the former initial verification. In place of the appropriate office of weights and measures, a conformity assessment body, selected by the manufacturer, which can still be an office of weights and measures confirms the conformity of a measuring instrument with the valid legal requirements through issuing a certificate of conformity.
On the basis of this, the manufacturer of the measuring instrument prepares a written declaration of conformity for the measuring instrument. Can mechanical dial thermometers with a CE marking be placed on the market? With CE marking, the manufacturer, the company or person placing the product on the market or the EU authorised representative declares that the product complies with all relevant European guidelines.
Since there is no binding instruction directive for mechanical thermometers in accordance with DIN EN , such instruments can also be placed on the market without a CE marking. A diaphragm seal is an additional component which protects a pressure measuring instrument or process transmitter. It transfers the medium to the measuring instrument without it coming into contact with the measuring instrument. When should a diaphragm seal be applied?
Diaphragm seals are used for pressure measurement when the proces medium doesn't come in contact with the pressure of the measuring instrument or when adjustment to the harsh conditions of a process is required. How does a diaphragm seal work? A diaphragm made of the appropriate material separates the medium to be measured from the measuring instrument. The internal space between the diaphragm and the pressure measuring instrument is completely filled with a system fill fluid.
The process pressure is transmitted by the elastic diaphragm into the fluid and from there to the measuring instrument.
With which instruments can a diaphragm seal be combined? A diaphragm seal can be combined with almost all pressure gauges, process transmitters, pressure switches or pressure sensors. What are the mounting options for a diaphragm seal? A diaphragm seal can be mounted via a direct connection, a cooling element or a capillary. In which application areas can diaphragm seal systems be used? How flexibly can a diaphragm seal be assembled? The optimal diaphragm seal designs, materials, filling media and accessories are available for each application.
Certificates can be supplied depending on the requirement. What is a diaphragm seal characteristic curve? The diaphragm seal characteristic curve shows a graphical representation of the elasticity of the diaphragm.
In this representation, the volume change is related to the pressure change and illustrated. When are flange connections used with diaphragm seals? The combinations of diaphragm seals with flange connections can be used for processes with extreme temperatures and with aggressive, adhesive, corrosive, highly viscous, environmentally hazardous or toxic media. With its connection dimensions, the flange-type diaphragm seal is suitable for all currently used standard flanges and is mounted in lieu of a blind flange.
How are the diaphragm seals connected? The diaphragm seals are available with female or male thread in their basic design. Due to the wide variety of available process connections they can be mounted to many different connections without any problems. Generally these connections are T-pieces which are integrated into a pipeline or welded to a pipeline by means of a welding socket.
When are sterile connections used with diaphragm seals? The combination of diaphragm seals with pressure measuring instruments in hygienic design can be used for processes with gases, compressed air or vapour and also with liquid, paste-like, powdery and hot media.
The diaphragm seals resist the temperatures that occur and meet the requirements for sterile connections. SIP and CIP criteria, which are an essential requirement for sanitary applications, are met by using diaphragm seals. These acronyms stand for the sterilisation and cleaning of the wetted parts in the process.
The combination of pressure measuring instruments with flush diaphragm seals or in-line diaphragm seals meets the stringent demands made on hygienic instrumentation and is suitable for even the most difficult measuring requirements. Why are there different materials or coatings with diaphragm seals? Various materials or coatings are available for diaphragm seals to allow accurate measurement of difficult media aggressive, corrosive, abrasive, highly viscous, heterogeneous, toxic, hot or aseptic.
Suitable materials or coatings are available for almost all processes. Why are there different system fill fluids with diaphragm seals? In selecting the system fill fluid for diaphragm seals, factors such as compatibility physiologically harmless and also temperature and pressure conditions at the measurement location are of crucial importance.
Depending on the system fill fluid, the appropriate minimum and maximum operating temperature range must be observed. What influence does the diameter of the diaphragm have on the display? Diaphragms with small diameters can only measure small volume changes. The larger the diameter of a diaphragm, the better the deviations that occur can be compensated for. How does a diaphragm seal system with capillary behave with height differences? A height difference between the pressure measuring instrument and the diaphragm seal affects the measurement.
This is due to the hydrostatic pressure of the liquid column in the capillary. The display is reduced when the pressure measuring instrument is positioned higher than the diaphragm seal. It is increased when the pressure measuring instrument is positioned lower. With the design of the entire system at the factory diaphragm seal and measuring instrument at the same height , this height difference must be known and taken into account accordingly.
How are diaphragm seals integrated into processes? Diaphragm seals are mounted to existing connecting flanges or welding sockets, which are welded to a pipeline, a process reactor or a tank. What is a diaphragm seal with an extended diaphragm and when are these used? The cell-type design is a sub-category, which is used with a blind flange at the tapping flange. Special designs can be manufactured to customer's specific requests.
What influence does the volume have on a diaphragm seal system? When connecting a diaphragm seal to a pressure measuring instrument, the diaphragm seal must deliver a working volume that is at least equal to the control volume of the pressure measuring instrument. Under real operating conditions, it must be considered that, through temperature and compressibility, the system fill fluid can change its volume.
How can the response time with a diaphragm seal system be influenced? The response time of a diaphragm seal is influenced by the viscosity of the system fill fluid and the configuration of the capillary.
What influence does temperature have on a diaphragm seal system? Temperatures in real operating conditions process and ambient temperature lead to volume changes in the system fill fluid. This, in turn, causes a pressure change in the closed system and thus display deviations.
What is the response time with diaphragm seal systems? It is dependent on the volume displacement in the entire system. When are threaded connections used with diaphragm seals? The combinations of diaphragm seals with threaded connection can be used for processes with extreme temperatures and with aggressive, adhesive, corrosive, environmentally hazardous or toxic media.
Electronic thermometers RTD's, thermistors and thermocouples measure the affects of heat on electronic currents. Resistance devices RTD's and thermistors take advantage of the fact that electrical resistance reacts to changes in temperature along predictable curves.
Both the thermistor and its high-precision "standards thermometer" cousin - the RTD - measure resistance in a resistor attached to an electronic circuit to calculate temperature. Thermistors typically use ceramic beads as resistors, while RTD's often use either platinum a highly stable metal or other metal films. With thermistors, resistance decreases with temperature and with RTD's, resistance increases. Both thermistors and RTD's may have a higher degree of accuracy than thermocouples, but their range is limited by comparison and they are generally not as fast.
Thermocouples work on the principle, that when connected to two different metals across a span with a temperature difference, an electronic circuit is generated. The voltage of the generated circuit changes with variations in temperature in predictable ways.
Temperature may be measured in Fahrenheit, Celsius or both. Some devices, such as meat thermometers , have a sensing probe. There are thousands of different thermometers available. One of the primary considerations should be the application requirements.
For industrial applications, shock resistance and vibration tolerance could be important. The temperature range and degree of accuracy required are also pertinent considerations.
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