What is an error in the pressure gauge?
- Inaccuracy in pressure gauge occurs when an output signal diverges from the desired value.
- When the pointer on the pressure gauge scale indicates a higher or lower value instead of actual.
What are the factors affecting accuracy and performance in Pressure Gauges?
- The majority of pressure gauges used are the bourdon tube type or diaphragm type having a pointer and dial arrangement for indicating the pressure
- During the selection and installation of the pressure gauge process temperature and ambient temperature is important to be considered.
The three factors that affect pressure gauge accuracy and performance:
1. Temperature:
- For the calibrated gauge the user may experience a 2% error in reading for every 30 °C temperature shift.
- This is due to variations in elasticity or spring rate of bourdon tube elements with temperature.
- This is caused by change in the elasticity or spring rate of the bourdon tube.
- But it is quite hard to overcome the influence of ambient temperature.
- To avoid gauge damage from the saturated heat source of steam service common practices such as
- Installing coil siphons or pigtail siphons to vanish the process heat.
- Installing a diaphragm seal with capillary to avoid high heat.
2. Vibration:
- Vibration due to pumps, motors, and other rotating equipment causes excess wear and unseasonable damage to the pressure gauge’s internal parts such as the bourdon tube and gear mechanism.
- Pointer oscillation caused by continuous exposure to vibration makes it difficult to accurately gauge reading.
- This difficulty is solved by using a liquid-filled pressure gauge. The liquid used is either glycerine or silicone.
- Liquid-filled gauge protects and lubricates the movement of the internal gear mechanism.
3. Pulsation:
- The pulsation effect occurs around pump discharge and quick operating valves. Liquid (Glycerine or Silicone) filled gauge reduces the effect of pulsation
- Pulsation reducer such as pistontype snubber or sintered metal snubber are installed at the upstream side of the gauge socket.
- To address pulsation in the gauge a needle valve is slightly opened or pinched down at the upstream side of the gauge.
- But for addressing the pulsation effect the needle valve is not recommended because the user may accidentally open the valve, thereby negating restriction in fluid flow.
- To address pulsation
- A clean or low viscousfluid like gases or liquids, a threaded orifice flow restrictor, or a sintered metal snubber is usually installed.
- In dirtier and higher viscosity fluids like massecuite or oil, a piston snubber is usually installed.
What are the common reasons for Pressure Gauge Failure?
1. Mechanical vibration:
- Vibration is an irregular oscillation of mechanical parts.
- In most cases, pressure gauge failure occurs during mechanical vibration in the system. It has a negative impact on gauge accuracy.
- Vibrating gauge makes difficult to read the pointer location on a dial.
- Incremental damage to the pointer mechanism produces inaccurate readings.
Indications
- Detached pointer if the vibration is severe
- Metal erosion or dust inside the gauge window from worn pinion and segments gears.
Risks
- Wear and tear of internal components
- Loss of accuracy and functionality
- Pressure system failure
2. Pulsation Effect:
- It is the regular occurrence of rapid increase or decrease in pressure of the flowing media.
Indications
- Pointer vibration
- Loose or broken pointer
Risks
- Difficult to obtain an accurate reading.
- Wear and tear of internal components.
- Loss of accuracy and functionality
- Pressure system failure.
3. Extreme Temperature:
- Generally, the gauges we are using have various tolerances for extreme temperatures. We observe both ambient temperatures and the temperature of the process media.
Indications
- Liquid or Dial is discoloured, usually yellow, orange, brown, or black.
- Dial, the Case is melted due to high-temperature media.
Risks
- Difficulty in obtaining an accurate reading
- Loss of accuracy and functionality
- Pressure system failure
4. Pressure Spikes:
- These spikes occur when the pressure rises sharply and drops suddenly.
- Spikes cause some sort of problems for gauges that are not designed for a particular application or condition.
Indications
- Pointer damage
- Bending of a pointer like a fishtail or fish hook from hitting the stop pin too hard
- Stop pin broken.
Risks
- Increased wear on movement and components
- Loss of accuracy/functionality
- Split Bourdon tube, leading to released media
- Pressure system failure.
5. High or over Pressure:
- This condition is somewhat similar to pressure spikes.
- This occurs when the gauge measures a pressure of maximum range.
- Generally, this overpressure is observed in water or wastewater treatment and gas lines.
- The effect of overpressure causes the Bourdon tube to twist.
Indications
- Pointer buried against stop pin
- Pointer dislodges stop pin
Risks
- Loss of accuracy and functionality
- Damages Bourdon tube
- Pressure system failure.
6. Corrosion Effect:
Most process industries work with harsh chemicals such as
- Hydro fluoric acid in refineries
- Flocculants andChlorine in wastewater treatment.
- Chlorinated gases in fibre optic products.
Indications
Stain in the gauge case, pointer, connection, and dial.
Risks
- Loss of accuracy/functionality
- Pressure system failure
7. Clogging or Jamming:
- Jamming is a major issue because a slurry, viscous, and dust media may block the system.
- This occurs in major industries such as paper plants, wastewater treatment plants, pharmaceuticals, and other industries
Indication
Indication at zero or near zero position during system operation hour.
Risks
- Loss of accuracy
- Possibility of overpressure
Which devices are used to calibrate the pressure gauge?
The pressure gauge can be calibrated by using tools like
- Dead Weight tester
- Standard Pneumatic calibrator
- Calibrator with an accurate reading.
How do you calculate pressure gauge error?
Error in pressure gauge for each pressure can be calculated by using the relation
What are the four 4 types of pressure measurement?
- Gauge Pressure.
- Sealed Pressure.
- Absolute Pressure and
- Differential Pressure.
What is the error of the pressure gauge?
Pressure measurement errors:
What are the types of errors in the Pressure Gauge?
The specific types of errors
- Zero Point Error: An Initial point of measurement range is too high or too low, thus shifting the entire scale up or down by zero offset value.
- Span Errors : It is actual distances between the individual divisions from the zero point to the full scale are even but have a wrong value with magnifying error effect at the upper end of the scale.
- Nonlinearity: It is the actual distances between the individual divisions from the zero point to the full scale that are non-linear or not even thus making the ideal straight line into a curve.
How to correct zero error in pressure gauge?
- Zero error is corrected by releasing the pressure by opening the sealed vent.
- Note that re-sealing the vent is done to avoid oil leakage and gauge damage.
- Due to variations in temperature and elevation, the pressure inside the gauge will build up and affect the needle settings to zero.
Why is it important to calibrate a pressure gauge?
- To ensure accurate measurement of pressure the gauges are required to be calibrated at regular time intervals.
- Using inaccurate or un-calibrated gauges causes safety issues, production downtime, or faulty products.
