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FAQs

Frequently Asked Questions

  1. Pressure Gauges
  2. Transmitters/Transducers
  3. Digital Indicators
  4. Valves
  5. Temperature
  6. Diaphragm Seals

Pressure Gauges

Transmitters/Transducers

Digital Indicators

Valves

Temperature

Diaphragm Seals


Pressure Gauges


Q: What is the purpose of the ventable & non-ventable fill plug/relief plug?
A: A fill plug seals the fill hole in a pressure gauge case. On liquid filled pressure gauges, a ventable fill plug is used to relieve internal case pressures that occur due to thermal expansion of the fill fluid. In non-filled dry gauges, a non-ventable fill plug is used to occasionally drain the interior of the case from condensate or relieve internal case pressures. Ventable fill plugs incorporate a vent pin to open and close a hole for relieving internal case pressures and do not have to be removed from the case hole like non-ventable fill plugs.

Q: What are the designed overpressure ratings for NOSHOK gauges?
A: Overpressure ratings are specific to the gauge type, pressure range and accuracy ratings of the gauge. Normal overpressure protection can range from 1.1X to 1.3X depending on the gauge selected. NOSHOK gauges comply to the EN-837-1 and ASME B40.100 standards in regards to overpressure protection. When selecting a pressure gauge, it is recommended that the normal system pressure be maintained around half of the full range of the gauge as to avoid overpressure conditions.

Q: How is the accuracy of a gauge affected by a Maximum Indicating Pointer?
A: A Maximum Indicating Pointer (MIP), also commonly referred to as a Tell Tale Pointer, adds an additional error to the pressure gauge due to the increase load on the bourdon tube. The lower the pressure range, the higher the error. Typically 1%. Consult factory.

Q: What is a Certified Calibration?
A: Certified Calibrations provide the user with a serial numbered gauge along with a calibration certificate that it has been certified in accordance to the pressure gauge standard with instruments that are traceable to NIST with accuracies of at least 4 to 1.

Q: What is a Certificate of Conformance?
A: A Certificate of Conformance is a formal statement on company letterhead stating that an instrument complies with a particular standard and/or specification. It contains the signatures of the required personnel. These Certificates are often needed to show industry inspectors that a system and its components are in compliance.

Q: How often does a gauge need to be calibrated?
A: NOSHOK pressure gauges require little or no calibration within the Warranty period. Some applications may be more aggressive than others, resulting in an increased frequency in the need for calibration. The environmental limitations for the pressure gauge series should be observed in all cases. Gauges used in situations outside these requirements may result in inaccuracies, premature wear and/or failure of the gauge and would require additional maintenance. The frequency of calibration, therefore, is best left to the user to determine.

Q: When is it recommended to use an orifice?
A: Orifices are a type of snubber. On pressure systems that have rapidly increasing or decreasing pressure spikes, orifices lessen the effects of these energy pulses by blocking the wave energy using restricted flow. They are recommended in dynamic pressure applications with mild pressure spikes.

Q: When is a diaphragm seal used, and when would you apply a diaphragm seal and capillary?
A: A diaphragm is used to isolate and protect the instrument from the process media. Damaging process media may include corrosives, particulates, temperatures, or any state that is not suitable for direct contact with the measuring element. Diaphragms indirectly transmit system pressures by segregating the process pressure with a thin flexible membrane that in turn transfers the pressure through a fill fluid to the instrument. Diaphragms are often used in conjunction with capillaries to further distance the instrument from the process media. Capillary tubes transmit the diaphragm fill fluid to the instrument. Capillary tubes come in several lengths and provide the user a means to measure in a remote location and may also act as heat dissipaters in high temperature applications.

Q: What is the purpose of liquid filling a gauge, and in what applications would a liquid filled gauge be used?
A: Primarily, in applications that have vibrations or pulsations, liquid filling enables reading the dial pointer by dampening the movement. Liquid filling should be considered in any system that has high dynamic operating conditions. In general, liquid filling helps extend the life of a gauge. It reduces damaging resonance induced fracturing, reduces frictional wear, prevents aggressive ambient air from entering, prevents condensation formation, and improves reliability.

Q: How does temperature affect the accuracy of a pressure gauge?
A: Temperature changes affect the stiffness of a bourdon tube. The stiffness change is produced by a combination of changes in the elastic (Young’s) modulus and a change in linear dimensions due to linear expansion and contraction. The error caused by temperature change will follow the approximate formula:
± 0.04 x (t2 – t) % of the span.

Q: How do you size a pressure gauge relative to process pressures, normal operating pressures, and maximum pressures in the process? (Dynamic or static process pressures)
A: The pressure range of a gauge should be a minimum of 10% over the maximum working pressure in static conditions (no pressure fluctuations). In dynamic conditions, the gauge range should be a minimum of 40% over the maximum working pressure. Ideally, the pressure gauge range should be selected for a midscale reading during normal operating pressures.

Q: What does a gauge accuracy statement really mean? (Examples: 1% of span, 3-2-3 percent of span)
A: Accuracy is the difference between the true value and the gauge indication expressed as a percent of the gauge span. It is determined by comparing a gauge indication to a known standard or certified true value and combines the effects of method, observer, apparatus, and environment. Accuracy error also includes hysteresis and repeatability errors. An ASME B40.1 class B gauge has three accuracies. For example, a 3-2-3 percent of span designation stands for 3% in the first quarter of the scale, 2% in the middle half of the scale and 3% in the upper quarter of the scale.

Q: What applications require the various lens materials, and to what maximum temperature can each be subjected?
A: Lens materials include Instrument Glass, Laminated Safety Glass, Tempered Glass, and plastic. Glass lenses are used for abrasion, chemical and wear resistant properties. Laminated safety glass reduces the possibility of shattering if the bourdon tube ruptures. Tempered glass is 2 to 5 times stronger than plain glass. Plastic lenses are used for impact, corrosion and chemical resistance. Special attention should be paid to the temperature and corrosive environments. Polycarbonate is selected for its superior impact resistance, acrylic for its clarity and scratch resistance and Homalite for its superior chemical resistance. In general, gauges with plastic lenses should remain below 140° F.

Q: In what situation would a pigtail syphon be used?
A: Pigtail syphons should be used in steam applications and systems that contain superheated vapor. The pigtail buffers the instrument from the damaging effects high temperature steam by holding system fluid in the coil to provide a steam trap for the fluid to condensate and dissipate the heat.

Q: What is the application for a gauge cleaned for O2 service?
A: Cleaning for Oxygen (O2) service is performed on gauges that are used on oxygen service or oxidizing media applications. The cleaning removes all hydrocarbons (oil and grease are common hydrocarbons) that can react violently, resulting in explosions, fire, and injury to personnel and property. Gauges cleaned for Oxygen service can be used in any application that requires the cleanliness level associated with oxygen cleaned gauge. Glycerin filled gauges cannot be used on oxygen systems or on other oxidizing media.

Q: What fill fluids options are available, and in what applications would each be used?
A: Glycerin is the most common fill fluid. Because of its unique fluid properties, Glycerin has become the standard for liquid filled gauges (see “What is the purpose of liquid filling a gauge?”). Glycerin’s clarity, viscosity, stability, cost, solubility, low toxicity make Glycerin an ideal fluid for many applications. Mineral oils and silicone fluids are used when temperature extremes, chemical compatibility or viscosity fall outside of Glycerin use. Halocarbon is an inert fluid that is compatible with chlorine, oxygen service some high temperature applications. Keep in mind that Glycerin is not compatible with strong oxidizers such as oxygen, chlorine, hydrogen peroxide, or nitric acid. Glycerin & Silicone are explosive in contact with chlorine. Halocarbon is explosive in contact with aluminum and magnesium.

Q: What is the difference between the ASME B40.1 and EN 837-1 specification?
A: The American National Standards Institute (ANSI) approves American National Standards which include the American Society of Mechanical Engineers (ASME) standard ASME B40.100. This Standard (B40.100) is confined to analog, dial-type gauges, which, utilizing elastic elements, mechanically sense pressure and indicate it by means of a pointer moving over a graduated scale. The European Committee for Standardization (CEN) is the officially recognized European standards body that develops European Standards (ENs) which include EN 837-1. The EN 837-1 includes mandatory dimensions, metrology, and testing requirement for sale in the European Union. ASME B40.100 includes similar requirements in a mandatory appendix.

Q: What is the purpose of throttle devices such as throttle plugs and screws?
A: Throttle devices limit the flow to the pressure instrument. They are a type of snubber.

Q: What is the purpose of an over and under load stop in a pressure gauge?
A: The tip motion of a bourdon tube is translated to rotary motion of a pointer by a linkage and sector gear acting on the pointer pinion gear. Stop pins limit the movement of the bourdon tube, sector or pointer rotation in over and under pressure conditions that would otherwise move the pointer pinion off the sector gear which would damage the gauge.


Transmitters/Transducers

 

Q:What is the difference between a transducer and transmitter?
A: When these terms originated there was a distinctive difference between the two. A transmitter was referred to as an instrument with a current signal (i.e. 4 mA to 20 mA) and a transducer was referred to as an instrument with a voltage signal (i.e. 0 Vdc to 10 Vdc). As time has progressed these terms are now commonly interchanged for reference to either output signal.

Q: What is the difference between the proof pressure and burst pressure specifications?
A: Proof pressure, which is higher than the full scale pressure point, is the limit that you can go to without affecting the performance and calibration of the transducer. The burst pressure, on the other hand, is the limit that you can go to before there is pressure chamber rupture and damage. An overload limit specification used sometimes means that proof and burst ratings are identical.

Q: What does RFI, EMI and ESD mean related to pressure transducers and transmitters?
A: Radio Frequency Interference (RFI) and Electromagnetic Interference (EMI) refer to the effects electrical noise can have on instruments. RFI frequently comes from hand held walkie-talkies and EMI comes from AC motors in the vicinity of the instrument. ESD (Electrostatic Discharge) comes from many sources including the application itself. CE compliant transmitters and transducers incorporate protection techniques and components to minimize most of the interference.

Q: Can traditional diaphragm seals or gauge protectors be used with pressure transducers and transmitters?
A: Most diaphragm seals can be used with pressure transducers and transmitters. The real key is to assemble and fill the seal properly, being careful not to entrap air in the fill fluid.

Q: Are pigtail steam syphons used in transmitter applications?
A: The steam syphon is necessary in steam pressure applications. It is important to isolate the transmitter sensing diaphragm from the high temperature encountered with steam pressure applications.

Q: Can orifices and snubbers be used and why would they be needed?
A: As with other pressure measurement instruments including gauges, pressure pulsations and spikes, are issues with pressure transmitters. Whenever the pressure of an incompressible fluid is measured, there is the potential for pulsations and spikes, which can damage pressure transmitters. An orifice installed in the pressure connection by NOSHOK can protect the transmitter from damage. Where there is the possibility of clogging the small orifice, an attachable piston snubber is recommended.

Q: What is the reason for the vent tube in the cable of the series 612 and 627 submersible level transmitters?
A: All pressure measurements are inherently differential in theory. Gauge pressure is referenced to ambient atmospheric, absolute pressure is referenced to vacuum contained in an evacuated chamber within the transmitter. The level measurement is also a differential measurement, with its reference to ambient atmospheric pressure. In order for the submersible level measurement to be referenced to atmospheric, the cable contains a vent tube which runs the complete length of the cable and “vents” into the atmospheric pressure at the junction box connection which is out of the liquid.

Q: How does the series 612 and 627 submersible level transmitter measure level?
A: The transmitter measures the hydrostatic pressure produced by the liquid level higher than the point where the instrument is located. The higher the liquid, the higher the pressure.

Q: NOSHOK transducers and transmitters are normally 2 wire or 3 wire in output configuration. Is a 4 wire transducer available?
A: Voltage output transducers are available with a 4th connection which is electrically the same as the power supply common to connect to wiring configurations that require it.

Q: What is the advantage of having a transmitter designed with a smaller diaphragm, and the pressure and temperature sensors positioned close to the media?
A: A smaller diaphragm is less easily damaged, and positioning the sensors directly behind the diaphragm minimizes fill fluid and enables active temperature compensation directly at the point of measurement.

Q: What is a turndown ratio?
A: A turndown ratio is also commonly known as rangeability, and refers to the ratio between the full-scale range and the minimum point of measure, indicating the range in which an instrument can accurately measure the media. Example: a pressure transmitter has a maximum calibration range of 0 to 300 psi, and a turndown ratio of 10:1. This means that the span can be adjusted anywhere between 0 to 30 psi and 0 to 300 psi. The higher the turndown ratio, the higher the rangeability, which can also minimize required inventory.


Digital Indicators

 

Q: Will the series 1800 Attachable Loop Indicator work with transmitters not made by NOSHOK?
A: The series 1800 indicator will work with any brand that has the same pin connections and style Hirschmann connector and sufficient power supply voltage to drive all instruments in the loop. The series 1800 will use 3 Vdc to operate.

Q: What is difference between loop powered & built in power supply?
A: 
A loop-powered device usually receives its power from an analog process signal connected to it through a transmitter loop, without requiring a separate or independent power source. These devices are designed to use the power from the current flowing in the loop and are simple, easy to wire and use very little power. A key benefit of loop power is that the voltage drop in the wiring does not affect the accuracy of the signal.

A device with a built-in power supply generates its own power, so no external power is required. These sensors are powered by the conductor wire running through the sensor aperture, providing an easier installation as a power source and additional wiring are not needed. Only the output is wired to a control or alarming device.

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Valves

 

Q: When should EPDM (Ethylene Propylene), FFKM (Kalrez®) or NBR (Buna N®) o-rings be used in valves?
A: The choice between alternative o-ring elastomers is based on specific application parameters that primarily include chemical compatibility and temperatures. For example, FKM may be used on higher temperature applications, or applications that require a broader range of chemical resistance than EPDM.

Q: What are the differences between FKM (Viton®), PTFE (Teflon®) and Grafoil®, and when should each be recommended?
A: FKM (Viton®), PTFE (Teflon®) and Grafoil® are selected depending on the customer application. The customer will often designate what material is required for their application. This usually involves process parameters such as media, pressure, temperature and chemical compatibility. NOSHOK would not recommend any one material, but would be available to assist in the selection process.

Q: What are the differences in regulating stems and stem tips?
A: A regulating stem is typically a tapered stem for metering and flow control applications. Stem
tips are often used for solid shut-off where high repetitions of opening and closing of the valve occur.

Q: What are the differences in each type of stem tip?
A:

Q: When and where should you use PTCFE (Neoflon®), PEEK (Ketron®), and Delrin®?
A: The choice between soft seat plastics, like o-ring elastomers, is application specific. Each plastic has its particular strengths depending on its wear resistance, chemical compatibility and heat resistance. Delrin® is a mid-range material with a superior wear resistance and a moderate heat and chemical resistance. PTCFE and PEEK are further up the pyramid, but each increase
in the range of properties has a price tag that follows.

Q: Why would you use an extended valve design (ex: 2070 Series)?
A: Utilization of the 2070, 2170 and 3070 Series is a matter of customer preference. The extended series offers a longer version for applications where more clearance may be needed in an installation. The operation of a standard length and extended length valve are identical.

Q: When do you require a double block & bleed vs. block & bleed?
A: Frequently, customers specify a redundant isolation block valve for safety in critical applications.

Q: What is a Dielectric Kit used for?
A: 
Dielectric Kits are designed to maintain the integrity and reliability of the pipeline and piping system through safety and corrosion protection. Dielectric Kits provide a non-conductive barrier between the process piping and the instrument and isolate components from the effects of electrical current. By eliminating metal-to-metal contact, current is halted to prevent corrosion and aid in the cathodic protection of the system. NOSHOK offers a single piece design Dielectric Kit and a two-piece design consisting of a PTFE sealing gasket and PVC dielectric shim for when a separate sealing gasket or o-ring is required.

Q: Why use a Stabilized Connector with an integral block valve?
A: 
Stabilized Connectors are designed to reinforce the entire installation by shifting radial-stress load away from the NPT connections. These Connectors are offered with an optional integral block valve, eliminating the potential of pressure shock to the measurement device.  The NOSHOK stabilized connecter with integral valve can be installed on either side of the stabilized body, allowing easy ½ turn installation for a level mounting surface eliminating any potential leak paths.

Q: Why use Futbols?
A: 
Futbols (flange adapters) bolt to the process side of a flange-flange manifold to allow connection of process flange taps or process root valves. Futbols also allow flanges to be connected to threaded process piping while maintaining the ease of removal or repair of the manifold if maintenance is required. The futbols provide a 1/16" offset connection from the bolt holes to give connection centers of 2", 2-1/8" or 2-1/4".

Q: Why use packing glands on valves?
A: 
Compression packing is a soft, pliant and resilient rope material, braided with various filaments or yarns, configured for inserting into a mechanical device such as a valve.  A PTFE stem seal provides a seal between the shaft of the handle stem and the valve body. This seal is then compressed around the stem by means of a packing gland, which forms a watertight seal around the handle stem assembly.  When used with compatible fluids, valves utilizing packing have a much higher pressure vs. temperature rating.

Q: Why use block & bleed valve vs standard valve?
A: 
Block and bleed valves are traditional isolation valves, consisting of “block” and “bleed” (vent) needle valves to isolate and vent downstream pressure. Block and Bleed Valves are used to keep a system pressurized with a fluid or gas while venting pressure only from the process side.

Q: When choosing a valve, why select Hard Seat vs Soft Seat?
A: 
Soft seat valves use a thermoplastic material such as PTFE, NBR etc. while hard seat valves use material such as 316 SS, Monel, etc. The key advantage of hard seat valves over soft seat valves is that they can withstand high temperatures and harsh service conditions.

In general applications, soft seat valves are suitable for use with clean fluid or gases and not recommended for use with dirty or viscous fluid, as particulates may damage the soft seat material and causing a leakage. If tight shut-off or bubble tight-shut off is required, a soft seat valve will provide superior sealing and shut-off capability in clean fluid applications.

Hard seat valves can withstand extreme flashing, hydraulic shock, abrasive process fluid, and ultra-high temperatures. In contaminated, erosive or corrosive fluid applications, a hard seat valve will provide better performance.


Temperature

 

Q: What is the maximum temperature rating on a bi-metal thermometer by itself?
A: 
Maximum temperature for a bi-metal thermometer in continuous use is 800°F but can be used in applications intermittently up to 1000°F.

Q: What is the definition of an RTD?
A: 
RTDs (resistance temperature device) are temperature sensors that are commonly used in a variety of industrial applications including industrial boilers, petrochemical, exhaust gas monitoring and food processing. RTD sensors have a higher accuracy than thermocouples and thermistors over a wide temperature range, and are more stable over time. Simply put, an RTD is a sensor whose resistance changes with temperature in a consistent repeatable manner.

Q: How does an RTD work?
A: 
An RTD can provide highly accurate and consistent temperature measurements because the change in resistance of certain materials is so predictable. Most RTD sensors have a response time between 0.5 to 5 seconds and commonly feature a platinum-based element, but can also be constructed with nickel or copper. RTDs made with platinum (also known as PRTs - platinum resistance thermometer) are used most often today due to their higher temperature capabilities, better stability and repeatability.

Probe type RTDs generally consist of a rigid probe with direct mounted connector or extension cable. Assembly type models usually incorporate a rigid probe assembled with a connection head (junction box). Direct immersion probes have the RTD protective sheath (the probe) welded to process fitting similar to temperature gauges - this offers better response but mechanical protection is limited. Access to a process under operation is also limited. Assemblies for Thermowells have the RTD probe typically spring loaded in the connection fitting - this ensures good thermal contact and removes dead space in well tip.

Q: Why and when would you use an RTD connection head?
A: 
An RTD connection head provides a clean, protected area for mounting a terminal block or transmitter, and can be rated for indoor or outdoor use providing protection against dust, rain, splashing and water from washdown hoses.  NOSHOK RTD connection heads are available in cast aluminum, white polypropylene, and cast 316 Stainless Steel. White polypropylene is popular for sanitary and chemical applications, while Stainless Steel is often used in food, pharmaceutical, biotech and chemical applications. Aluminum and Stainless Steel are preferred for industrial applications. Intrinsically safe explosion-proof enclosures are also available for hazardous environments.

Q: Explain the bulb dimensions on vapor actuated thermometers.
A: 
The physical principles of vapor actuation require that the dial face be printed with a nonlinear, progressively graduated temperature scale. These instruments are available for direct mounting, or for remote mounting with capillary lengths up to 100 feet. Sensing bulb length is dependent upon the capillary length selected (a longer capillary length will require a longer sensing bulb length).

Q: What is the best way to protect an instrument’s stem against high velocity flow?
A: 
A thermowell would offer additional protection and be the preferred method if the application allows for one to be installed.

Q: What is the difference between an adjustable union connection and a sliding compression fitting?
A: 
The sliding compression fitting can be used to adjust the immersion depth of the instrument’s stem.  The adjustable union connection can be used to reposition the dial face and for better viewing.

Q: Why are thermowells used?
A: 
A thermowell is used with a temperature-sensing instrument to provide a protective barrier between the instrument and the process media. Thermowells can provide protection from harmful process influences including flow, high pressure and harsh environments, reducing the possibility of damage to the temperature instrument and providing protection to the operator.  Thermowells also allow easier service to the instrument and reduce operating costs by allowing the temperature instrument to be removed and replaced without shutting down and draining the process.

Q: What types of thermowells are available?
A: 
The most commonly used types of thermowells are threaded, socket weld, weld-in and flanged connections.

  • A threaded thermowell is screwed directly into the process through the tapped pipe wall or via a thermowell threadolet
  • Socket Weld thermowells can be welded directly into the socket of the weldolet or into the wall of the pipe
  • Weld-In Thermowells are welded directly into the piping or a process vessel
  • Flanged thermowells incorporate a flange collar located on the mating flange, which is paired with a pipe nozzle

Q: What is lagging extension on a thermowell?
A: 
A lagging extension, often referred to as the thermowell’s “T” length, is located on the cold side of the process connection and is usually an extension of the hex length of the Thermowell. Usually the lagging extension enables the probe and thermowell to extend through insulation or walls.

Q: How do you calculate the stem length of a thermowell?
A: 
The bore depth “S” of a thermowell can be used as a reference for the maximum stem length. The “S” must equal or exceed the length of the sensitive portion of the instrument's stem.

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Diaphragm Seals

 

Q: What factors are important when selecting a diaphragm seal?
A: 
Utilizing diaphragm seals with instruments is recommended when instrumentation is to be used in corrosive process media or extreme temperature media environments. Important factors to consider when selecting the correct diaphragm seal for a specific application include:

  • The instrument’s location
  • The instrument’s process connection size and type
  • Process pressure and temperature limits
  • Any nontechnical fill fluid limitations (i.e. nontoxic fill fluids for sanitary applications)

Q: What factors are important when selecting a diaphragm seal fill fluid?
A: 
Process media compatibility is a key factor to consider when selecting a Diaphragm Seal fill fluid.  Process media temperature and should also be taken into account as all fill fluids expand or contract with temperature variations. It is important to note that the fill fluid viscosity and density are directly related to the measurement response time. The more viscous the fill fluid, the longer the response time. A higher density fill fluid may affect mounting as well.

Common Diaphragm Seal fill fluids include glycerin, silicone oils and halocarbon, but NOSHOK offers many more options including Neobee M20, Mineral Oil and Propylene Glycol for specialized applications. Glycerin should not be used for vacuum and compound gauges, or where a capillary is used between the instrument and Diaphragm Seal.

Q: How does a diaphragm seal work?
A: 
A diaphragm seal is designed to provide protection from corrosive, viscous, contaminated or very high temperature process media to valuable instrumentation. The pressure measuring element of the measuring device and the instrument connection port are filled with a suitable liquid, utilizing vacuum filling technology, making pressure measurement a direct and simple process. Pressure, when applied to the surface are of the diaphragm, causes a pressure increase in the fill fluid which is then transferred to the attached pressure gauge, transducer, switch or other pressure measuring instrument.

Q: What type of instruments can be mounted to a Diaphragm Seal?
A: 
Diaphragm Seals can be used with pressure gauges, pressure transducers/transmitters, and electronic pressure switches.

Q: What accessories are available for use with Diaphragm Seals?
A: 

  • Cooling Elements work in combination with diaphragm seal to isolate instrument from high media temperatures and are recommended for process temperatures above 212 °F. They provide effective temperature reductions of 200 °F depending upon ambient conditions and require a direct mounted system.
  • Stainless steel capillaries with or without stainless steel armor can be used to protect the instrument from high or low process temperatures and allow remote mounting of pressure instrument(s). Select the shortest capillary length possible, as changes in ambient temperature conditions may significantly affect the accuracy and response time of the instrument.
  • Sanitary Clamps & Gaskets (for NOSHOK Type 12 Seal only) available in NBR, EPDM, PTFE and FKM, meet FDA and 3A sanitary standards

 

Q: What affect does seal have on accuracy of the measurement?
A: 
In general, the diaphragm adds ½% to the instrument at room temperature.  There are also additional thermal errors that need to be calculated depending on the application.  NOSHOK provides a thermal error calculation here: https://www.noshok.com/images/diaphragm_seals/DiaphSeal_Thermal_Error_Calculations.pdf

Q: How is the capillary fill fluid internal pressure determined? if a diaphragm bursts what will happen to the transmitter out let pressure?
A: 
The fill fluid pressure is equal to the application pressure.  If a diaphragm bursts, the fill fluid will be dispersed into the process media and the instrument will be submitted to the pressure of the process media.

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