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Measuring level with differential pressure and a wet reference leg: correctly calculate wet leg, density and zero shift

The level in a closed process vessel is to be measured using a differential pressure transmitter. The high-pressure side is connected to the lower vessel connection...

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Vortex flow measurement with wet steam: identify condensate and steam quality as sources of error

A vortex flowmeter appears to operate reliably in a steam line for months. Pressure and temperature are within the expected range, the indication is stable...

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Monitoring a dual sensor in a temperature transmitter: detect sensor drift through the deviation between two Pt100 sensors

At a critical process measuring point, two Pt100 sensors are installed in the same measuring insert. Both measure almost the same temperature and are evaluated by...

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Diaphragm seals with two capillaries on a differential pressure transmitter: design line lengths and temperature effects symmetrically

A differential pressure transmitter is connected to a closed process vessel using two diaphragm seals. The lower measuring point detects the pressure from...

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Comparing compressed-air leak rates at different network pressures: reference measured values to a common condition

During a compressed-air audit, a leak rate of 63 Nl/min is measured at a leaking fitting. A few weeks later, the same point is checked again and the measuring...

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Dose rate meter at different radiation energies: understanding detector energy dependence

A dose rate meter is checked using a known gamma source and displays a plausible value. The same instrument is then used near an X-ray system, another radionuclide...

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Emptying an SF₆ filling hose after filling: consider hose volume, residual gas and gas recovery

An SF₆ switchgear system has been filled to the specified gas condition, the filling pressure or gas density is correct, and the system valve is closed. The actual filling...

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Conductivity sensor shows drift: systematically check electrode deposits, polarisation and cleaning

A conductivity sensor has been commissioned correctly, the cell constant is set and initially the measured values agree with a reference. After a few days or weeks, however...

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Measuring the thermal mass flow of hydrogen with changing purity: consider gas composition as a measurement error

A thermal mass flow meter shows stable values in a hydrogen system over a long period of time. Then the gas quality changes: after an electrolyser is started...

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Installing a SITRANS clamp-on sensor on coated pipes: consider paint, wall thickness and coupling point

Clamp-on ultrasonic measurement is particularly suitable for existing pipelines because the sensors are mounted externally and the pipe does not...

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Installing the flexible capillary on a Dynisco sensor: observe bend radius, strain relief and clearance from heater bands

Installing a melt pressure sensor with a flexible capillary initially appears straightforward: the rigid sensor stem is screwed into the mounting hole of the...

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Sizing Edge Buffer Storage: Calculate Offline Duration, Data Rate and Storage Reserve

An IIoT application runs reliably for weeks. Sensors and controllers send their measured values to an edge gateway, which forwards the data to a historian, SCADA...

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Correctly sizing the burden of a current transformer: consider VA rating, cable length and measuring device input

A current transformer has been selected to match the primary current, the transformation ratio is correct, and the connected measuring device also has the...

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Positioning a leakage current clamp correctly: measure a single conductor, all active conductors or the protective conductor?

A leakage current clamp is placed around a conductor and shows 6.8 A. Is this a dangerously high leakage current?...

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Bump test with incorrect gas flow: checking adapter tightness, flow rate and response time correctly

A portable gas detector is exposed to test gas before use. The cylinder contains the correct gas concentration and is still within its specified period of use...

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Using the Coriolis density value as a quality indicator: distinguishing process changes from gas bubbles

A Coriolis flow meter continuously monitors a liquid production stream. The mass flow initially appears plausible, but at the same time the measured density...

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Testing tyre inflator gauges without an external compressed-air supply: using the hand pump, buffer reservoir and fine adjustment correctly

A tyre inflator gauge is to be tested directly at a petrol station. However, no suitable compressed-air connection is available at the test location, or...

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Moisture in a load cell junction box: systematically checking leakage currents, signal drift and sealing

A vessel scale with four load cells suddenly develops a slowly drifting zero point after several years of operation. On dry days, the scale operates normally. After...

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NBR, FKM or EPDM in a MINIMESS test point: selecting the correct seal for the medium and temperature

A MINIMESS test point is used on a hydraulic system with mineral oil at 60 °C. A technically identical connection is then to be used on another system with...

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Pneumatic calibration with nitrogen or compressed air: correctly assessing cleanliness, moisture and supply

A precision pressure controller is to automatically calibrate pressure sensors up to 20 bar. Both a nitrogen cylinder and the plant compressed-air network are available...

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Installing a radar level sensor in an angled nozzle: correctly adjusting antenna alignment and reflection direction

An existing storage tank has a process nozzle welded into the roof at an angle. A radar level sensor can be mounted mechanically without any problem, but its...

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Dual Pt100 for redundancy: correctly planning two measuring inserts, two transmitters or sensor switchover

A temperature measuring point can be critical to the operation of a plant. If the Pt100 fails, the process value is suddenly no longer available. For this reason, a...

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Installing impulse lines for liquids: correctly managing gas bubbles, elevation differences and transmitter position

A flow measurement using an orifice plate operates with a differential pressure range of, for example, 0 ... 100 mbar. The differential pressure transmitter is...

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Measuring particles in compressed air: correctly accounting for pressure level, sampling and counting volume

A compressed-air line operates, for example, at 8 bar. To check the compressed-air quality, a sample is routed through a pressure regulator to an optical particle...

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Using a contamination probe with protective film: balancing protection of the entrance window against loss of sensitivity

A contamination probe is regularly used on dirty, wet or mechanically challenging surfaces. To protect the sensitive entrance window from damage or direct...

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Checking an SF6 gas density monitor after transport: assessing temperature equalization and pointer position before commissioning

A new SF6 gas density monitor is delivered in winter. Immediately after unpacking, the pointer in the depressurized condition is not exactly where it would be expected...

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pH measurement in ultrapure water: correctly handling low conductivity and unstable readings

A pH electrode is immersed in freshly produced ultrapure water. The measuring instrument has been calibrated correctly, the electrode works perfectly in the buffer

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Measuring dew point in high-pressure hydrogen: correctly accounting for sample pressure reduction and pressure dependence

The residual moisture in a hydrogen system is to be monitored. The H₂ in the process line is, for example, at 350 bar. For dew point measurement, a small gas...

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SITRANS FMS100 in plastic or lined pipes: correctly implementing grounding and equipotential bonding

A SITRANS FMS100 is installed in a plastic pipeline. The flow is stable, the pipe is completely filled and the conductivity of the medium is well above the minimum...

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Reusing a Dynisco sensor after removal: checking thread, diaphragm and sealing surface before reinstallation

A Dynisco melt pressure sensor is removed from the extruder during maintenance. At first glance, the sensor still appears complete and the electrical...

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Change-of-Value instead of a fixed transmission interval: choosing the right deadband for slowly changing measured values

A pressure sensor provides a new measured value every second. However, the process changes only very slowly. Over several minutes, for example, the value fluctuates...

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Shunt heats up under load: considering temperature coefficient and cooling as measurement errors

A DC circuit is monitored using a measuring shunt. Immediately after switch-on, the measuring instrument indicates, for example, 500 A. After several minutes of...

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Measuring the contact resistance of circuit breakers: test current, measuring points and reproducible contacting

During maintenance of a three-pole circuit breaker, the contact resistances of all three poles are measured. Pole L1 shows 42 µΩ, L2 44 µΩ and L3 initially...

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Selecting the right reference for tyre inflator pressure gauges: matching measuring range, accuracy and resolution to the test tolerance

A tyre inflator pressure gauge with a typical operating range of a few bar is to be tested. A digital pressure gauge with a measuring range up to 40 bar and...

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NDIR CO₂ measurement in humid process gas: taking water vapour, pressure and sample conditioning into account

The CO₂ concentration in a process line is to be determined using an NDIR measuring device. The gas contains, for example, 10 vol.% CO₂, is warm, nearly saturated...

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Stabilizing weighing electronics after switch-on: correctly assessing the warm-up time of amplifier and load cell

An industrial scale is switched on in the morning. Immediately afterwards, it indicates, for example, 0.00 kg with no load applied. Ten minutes later, the display...

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Residual pressure in the MINIMESS hose after disconnection: safely relieving trapped volume

A service technician measures a system pressure of 250 bar on a hydraulic system via a MINIMESS test point. After the measurement is completed, the...

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Pressure controller with multiple measurement modules: using auto-ranging and measurement uncertainty correctly across the pressure range

A calibration laboratory needs to test pressure sensors with measuring ranges of 0 ... 1 bar , 0 ... 10 bar and 0 ... 70 bar . A pressure controller with a 70-bar module...

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Radar level measurement in tall vessels: correctly planning antenna alignment, false echoes and signal margin

A storage tank is 35 m high and is to be monitored using a non-contact radar level transmitter. According to the datasheet, the selected device has a measuring range...

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Electromagnetic flow meter at very low conductivity: checking minimum conductivity, electrode contact and measurement stability

According to its datasheet, an electromagnetic flow meter is suitable for liquids with a conductivity of at least 5 µS/cm. The medium actually being...

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Pt100 characteristic curve according to IEC 60751: do not confuse α = 0.00385 with different characteristic curves

A Pt100 is tested at 0 °C and has a resistance of almost exactly 100.00 Ω. At first glance, everything therefore appears to be clear. Nevertheless, the...

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Testing tyre inflator pressure gauges with increasing and decreasing pressure: correctly assessing hysteresis and return to zero

A tyre inflator pressure gauge is compared with a reference at 2.0 bar and also indicates almost exactly 2.0 bar. At first glance, the instrument therefore appears...

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Operating three- and five-valve manifolds on differential pressure transmitters: using the equalizing valve and isolation sequence correctly

During normal operation, a differential pressure transmitter may measure only 120 mbar differential pressure, while a line pressure of 20 bar is present...

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Measuring oil content in compressed air: assessing aerosol and oil vapour as different contaminants

A compressed air system is monitored downstream of an activated carbon filter using a residual oil measuring device. The instrument displays, for example, only...

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Statistically evaluating contamination measurements: correctly interpreting counting time, count rate and detection limit

A contamination monitor initially shows 18 Ip/s on a surface, a few seconds later 23 Ip/s and during another measurement 20 Ip/s. Has the contamination actually...

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Distinguishing SF6 gas density and gas pressure during filling: understanding temperature compensation correctly

An SF6-insulated switchgear system is to be refilled after maintenance. The system documentation specifies, for example, a defined filling pressure...

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Assessing a pH electrode: identifying slope, zero point and aging from calibration

A pH electrode can still be calibrated successfully, but the process takes increasingly longer. In the calibration record, the slope is no longer approximately...

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Hydrogen pressure measurement with many load cycles: taking pressure cycling and measuring diaphragm fatigue into account

A hydrogen pressure sensor has a measuring range of 0 ... 400 bar and is used in an application in which the pressure regularly cycles between 30 bar and...

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SITRANS P320 with pulsating process pressure: correctly distinguishing electronic damping from real pressure peaks

A SITRANS P320 measures the pressure downstream of a pump. Without additional damping, the displayed value fluctuates continuously, for example between...

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Dynisco melt pressure sensor installed too deep or too shallow: correctly checking diaphragm position in the mounting hole

A melt pressure sensor is screwed back into the extruder after maintenance. The output signal is generally present, but it responds more slowly to process changes than before...

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Transmit measured value plus quality status: using Good, Bad and Uncertain meaningfully in IIoT data models

A pressure sensor has been reporting a constant value of 6.42 bar for hours. The trend in the dashboard looks completely stable. In reality, however, communication with...

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4–20 mA display in the current loop: calculating load, supply voltage and available loop voltage

A two-wire pressure transmitter is supplied with 24 V DC and sends its measurement signal to a 4–20 mA analog input of the PLC. The measurement works reliably...

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Micro-ohm measurement on busbars using four-wire technology: controlling contact placement and thermoelectric voltages

During maintenance of a switchgear system, the contact resistance of a bolted copper busbar connection is tested. The micro-ohmmeter initially indicates 8.4 µΩ...

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Catalytic LEL sensor after high gas concentration: correctly assessing overrange, recovery time and functional testing

A portable gas detector is exposed to a very high concentration of combustible gas during use. The display reaches 100 % LEL, indicates an overrange...

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Checking a load cell after shock overload: systematically assess zero point, linearity and mechanical stop

A heavy component accidentally falls onto a weighing platform. Afterwards, the scale is unloaded and the indication no longer returns exactly to zero, but instead...

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MINIMESS test point at very low pressure: consider check valve opening mechanism and measurement errors

A MINIMESS test point is used on a system to check a comparatively low pressure. The reference measuring instrument is suitable for the range, but it...

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Calibrating a pressure switch: check switching point, reset point and hysteresis in both directions

A pressure switch is supposed to switch at 6.0 bar. During the test, the pressure is increased slowly and the contact changes state at 6.08 bar. At first, the test...

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Radar level measurement in a stilling well: correctly considering pipe diameter, openings and deposits

A radar level sensor operates unstably on a vessel with a highly agitated liquid surface. An agitator, inlet flow or foam formation creates changing echoes...

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Electromagnetic flowmeters in partially filled pipes: correctly assessing electrode position, empty-pipe detection and measurement errors

An electromagnetic flowmeter shows a stable flow value even though an air pocket has visibly formed in the horizontal pipe. The electrodes of the flow...

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Grounded or ungrounded thermocouple: balancing response time, ground loops and electrical isolation

A Type K thermocouple is installed directly in a metallic machine component and is intended to detect rapid temperature changes. With a grounded measuring junction...

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Differential pressure transmitter shows zero point offset after pressurization: check line pressure effect and overload

A differential pressure transmitter initially indicates the correct value of 0 mbar when depressurized. The system is then subjected to line pressure...

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Measure pressure before and after the screen changer: detect contamination via differential pressure in extrusion

The melt pressure upstream of an extruder screen changer is increasing continuously. Is there a problem with the extruder, is the melt too cold, or is the screen pack becoming...

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MQTT QoS 0, 1 or 2 for measurement data: balancing delivery reliability and data volume

A sensor transmits its measured value to a broker via MQTT every second. Under normal operating conditions, this produces an apparently complete measurement series...

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Pneumatic Pressure Calibration After Rapid Pressure Changes: Consider Adiabatic Temperature Effects and Stabilization

During pneumatic pressure calibration, a test point is often approached as quickly as possible. A pressure controller may, for example, regulate from 0 bar to 10 bar within a short...

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Diffusion or Pump Gas Detector: Choosing the Right Sampling Time, Hose Length and Operating Mode

The available multi-gas detector has suitable sensors. Can the device simply be switched on at the vessel opening and held there for a few seconds? In many applications...

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Radar Level Sensor with Condensation: Correctly Assessing Antenna Buildup, Droplets and Signal Margin

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Load Cell Does Not Return to Zero After Unloading: Distinguishing Creep, Hysteresis and Mechanical Stress

A zero point that does not return completely can have various causes that must be assessed very differently from a metrological point of view...

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Coriolis Flowmeters with Abrasive Media: Correctly Monitoring Measuring Tube Wear and Zero-Point Trends

A Coriolis flowmeter has been measuring a solids-containing suspension for several years. The mass flow still appears plausible, but during regular zero-point checks...

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Gas-Actuated Thermometer with Remote Capillary: Correctly Planning the Capillary, Ambient Temperature and Routing

The temperature is to be measured on a hot pipeline, but the display must be located several meters away on an easily accessible control panel...

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Square-Root Extraction in Differential Pressure Transmitters: Correctly Scaling the 4–20 mA Signal for Differential-Pressure Flow Measurement

For a conventional differential-pressure flow measurement using an orifice plate, nozzle or Venturi tube, normally not. The reason is the physical relationship...

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Measuring PV I-V Curves: Detecting Shading, Mismatch and Defective Modules Using I-V Curves

According to the data sheet, a PV string has an open-circuit voltage of approximately 850 V. During testing, 842 V is measured – at first, everything appears...

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Measuring Ripple on a 24 V Power Supply: Tracing Sensor Noise and PLC Interference Back to the Power Supply

A pressure transmitter is actually providing a stable 4...20 mA signal, yet the analog value in the PLC fluctuates. A second sensor also shows sporadic jumps...

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Pressure Calibration Pump Does Not Generate Stable Pressure: Systematically Check Valves, Check-Valve Function and Seals

A hand-operated test pump is pressurized to 10 bar, the fine adjustment valve is no longer moved, and yet the reference pressure gauge slowly drops to 9.8 bar...

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Using a PID Gas Detector for VOC Measurement: Understanding Ionization Energy and Correction Factors

A PID gas detector displays, for example, 50 ppm VOC. Does this mean that 50 ppm of toluene, benzene or hexane is actually present?...

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Radar Level Measurement with a Low Dielectric Constant: Correctly Assessing Echo Reserve and Antenna Selection

Radar level sensors operate without contact and are therefore an attractive solution for many tanks and process vessels. With water, aqueous media or other...

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Operating Pressure Switches with Inductive Loads: Correctly Planning Contact Loading, Arc Suppression and Interposing Relays

A pressure switch is intended to switch a solenoid valve, contactor or relay when the set pressure is reached. The nameplate may state, for example, “10 A at 230 V AC”...

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Comparing PV string currents: Detecting partial shading, bypass diode issues and connection faults

Different currents in supposedly identical PV strings are a valuable indication—but not yet a definitive fault diagnosis. The current of a string is influenced...

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Condensing Measurement Data at the Edge: Combining Average, Minimum, Maximum and Raw Data Effectively

A sensor supplies one measured value every second. With 100 measuring points, this already produces 8.64 million values per day – even before timestamps...

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Calibrating a Pressure Sensor with Ascending and Descending Series: Evaluating Hysteresis Separately from Linearity Errors

A pressure sensor can indicate different values at 50% of its measuring range depending on whether the test point was approached from zero or from the upper...

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Selecting a Conductive Level Switch: Considering Minimum Conductivity, Electrode Spacing and Build-up

Conductive level switches are a simple and robust solution for detecting water and other electrically conductive liquids. They can be used for overfill protection...

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Ultrasonic Measurement in a V, Z or W Path: Choosing the Right Sound Path for the Pipe Diameter and Medium

In clamp-on ultrasonic measurement, the sensors are attached to the outside of the pipe. The pipe does not need to be opened or cut, and the sensors do not come...

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Protecting a Pressure Measuring Point Against Overpressure: Correctly Sizing the Overpressure Protector, Measuring Range and Safety Margin

A pressure measuring point operates reliably at 6 bar under normal conditions. However, when the system starts up, a valve closes rapidly or an operating error occurs...

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Ring Earth Conductors and Earthing Systems: Assessing Step and Touch Voltages During an Earth Fault

The measured earth resistance of an installation is low, and the connections of the ring earth conductor appear to be electrically continuous. Does this automatically...

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Generating Symmetrical ± Voltages with a Bench Power Supply: Connecting Two Outputs in Series Correctly

Operational amplifiers, instrumentation amplifiers, analog filters and many other analog circuits require more than a single positive supply voltage...

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SIL2 Melt Pressure Sensor in an Extruder: Correctly Planning Proof Testing, Diagnostics and the Safety Function

Melt pressure is one of the most important process variables in an extrusion system. Excessive pressure upstream of the screen, die or nozzle can indicate blockage...

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Dry-Block Calibrator with the Wrong Insert: Air Gap, Immersion Depth and Axial Uniformity as Sources of Error

A dry-block calibrator can control temperature very stably and still produce an incorrect calibration result. In such cases, the cause is often not the calibrator...

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Testing Circuit Breaker Timing: Measuring Opening Time, Closing Time and Pole Synchronism Correctly

A circuit breaker may appear electrically faultless while still operating mechanically too slowly, unevenly or with poor repeatability. Particularly with medium...

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Selecting a Frequency Converter for 50/60 Hz Testing: Correctly Sizing Voltage, Frequency and Load Type

An electrical device designed for 60 Hz cannot be realistically tested in Germany simply because a 230 V mains supply is available. For a reproducible functional test,..

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Monitoring a Reference Standard Between Calibrations: Using Check Measurements and Drift Limits Effectively

A valid calibration certificate confirms the condition of a reference standard at the documented calibration dates. However, it does not automatically guarantee that...

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Teaching a Capacitive Point Level Switch: Consider Dielectric Constant, Vessel Wall and Buildup

Capacitive point level switches can detect liquids, pastes, slurries, powders and bulk solids. Unlike a float switch, they do not respond to mechanical movement...

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Extending Load Cell Cables: Correctly Accounting for 4- and 6-Wire Technology, Sense Lines and Voltage Drop

Load cells often provide only a very small analog output signal in the range of a few millivolts. At the same time, the strain gauge measuring bridge must be supplied...

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Polarization Index PI and DAR: Correctly Assessing Insulation Condition

A single insulation resistance value of, for example, 500 MΩ initially only indicates the resistance of the insulation system at a specific point in time, at a specific...

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Glycerin or Silicone Oil in Pressure Gauges: Choosing the Right Filling Liquid

Liquid-filled pressure gauges are mainly used where vibrations, pulsating pressures or mechanical shocks cause the indication of an unfilled pressure...

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Insulation Testing of Long Cables: Consider Charging Time and Safe Discharge

Long electrical cables do not behave like a simple high-resistance load during an insulation test. Electrical capacitance exists between conductors, shield...

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Correctly Sizing Inverters for Motors and Inductive Loads

An electric motor with a rated power of 800 W cannot automatically be operated reliably with an inverter rated for 1,000 W continuous power. During startup...

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Timestamps for IIoT Measurement Data: Sensor, PLC or Gateway?

A measured value without a reliable time reference is often of only limited use in an IIoT application. This becomes particularly apparent in the case of faults...

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Height Difference in Pressure Calibration: Calculating Head Correction Correctly

During pressure calibration, the reference and the device under test should ideally be located at the same hydraulic or pneumatic reference height. In practice, however...

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Measuring Compressed Air Consumption Correctly: Understanding Nm³/h and m³/h

Compressed air consumption can only be evaluated unambiguously and compared between different measuring points if it is clearly defined which pressure and...

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Pt100 Insulation Faults: Diagnosing Moisture in the Sensor Correctly

A Pt100 can still provide an apparently plausible resistance value electrically while measuring incorrectly if the insulation between the measuring circuit and the metallic...

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Variable-Area Flowmeter with Limit Switch: Monitor Min./Max. Flow

A variable-area flowmeter with limit switches combines a directly readable local flow indication with simple electrical min./max. monitoring, without necessarily requiring...