Pressure transmitter calibration-FAQ

 

Instruthinkis a registered company by ISO who deal with the technicalities of pressure transmitter calibration. We are among the earliest manufacturers selling flowmeters, limit switches, and pressure transmitters. Different technical teams are available for testing, calibrating, and supplying the pressure transmitter. Now, let’s go through the pressure transmitter calibration procedures.

How is an absolute pressure transmitter calibration?

 

You can use the absolute pressure transmitter in different manufacturing processes for monitoring and transmitting the liquids with the pressure of liquids, steam, and gases. Therefore, the pressure transmitter calibration is essential to do manufacturing accurately and perform it occasionally. Follow the steps below for absolute pressure transmitter calibration:

• Close the isolation values from both sides of the pressure transmitter and again pressurize the line by opening the release valve.
• Attach the hose of the pressure transmitter with the NPT pressure port placed on the pressure transmitter in a clockwise direction until and unless it gets tight.
• Join the black lead of the pressure transmitter with a negative testing terminal available on the pressure sensor and the read information with the positive testing terminal.
• Press the “ON” button of the pressure transmitter. Then, by turning in the clockwise direction, you can open the pressure calibrator’s vent and press the “zero” button of the pressure transmitter. Now, you can quickly close the vent by turning again in a clockwise direction.
• You need to press the “UNITS” button, so the display starts to show “PSI.” Press the “ZERO” button to close the bleed valve. Switch to pressure vacuum valve for the “+” positive pressure.
• Keep pushing the hand pump inside and out until the display shows the reading of 3 psi. After pressing the “HOLD” button, note down the tasks of psi and mA visible on display. You have to keep repeating this process to collect mA for 9psi and 15psi.
• In the last step, you have to compare the readings with the specifications received from the manufacturer. Then, follow the instructions of the manufacturer for adjusting the pressure transmitter.

What are the procedures for pressure transmitter calibration?

 

Pressure is such a significant physical quantity that you can’t ignore it at any cost. So, industries use pressure transmitters for maintaining, controlling, and monitoring them at particular readings. You need a multimeter, pressure transmitter, and HART multimeter for pressure transmitter calibration.

Simple process for pressure transmitter calibration:

• First, isolate the pressure transmitter from the processing
• You need to gradually open the vent plug and vent value to release the pressure.
• Connection of the multimeter is with the transmitter, and make sure that the output is 4mA whenever you apply the pressure 0.
• Connect the pressure source (that is, the handheld testing pump) with the transmitter
• Also, check that there is no leakage.
• Keep applying the pressure at various ranges for checking the error.
• You need to do calibration if any error exists.

If the pressure transmitter is an analog transmitter:

• Apply the pressure at 0% (on the LRV) with the help of a handheld pump. You must check the multimeter if there is no 4mA and fit the zero pot inside the transmitter. Your result must be 4mA as the output from the transmitter
• Apply the pressure at 100% (on the URV) and receive 20mA inside the multimeter by adjusting the span pot in it.
• Keep repeating the above steps for the rectification of the error.

Figure 1 analog transmitter

If the pressure transmitter is a SMART transmitter:

• The HART communicator needs to connect with the transmitter. Select the menu for trimming the upper and lower range
• Basic setup calibration sensor trim/zero trim trimming upper or lower range valves
• The calibration is entirely automatic with the help of the HART communicator
• Restoration of the process connectivity
• Take the pressure transmitter on the line to ensure there is no leakage.

Figure 2 HART communicator

How to select the calibrator for the pressure transmitter?

• To receive accuracy according to the requirement:

Firstly, the determination of the highest level of accuracy is required to achieve according to the calibrating of the pressure transmitter. According to the standard, there is a recommendation of 10:1in the accuracy difference between pressure calibrator and pressure transmitter. Sometimes, it is not mentioned in the manufacturer’s specifications and can be better than your requirements. However, it is not such a parameter that you can ignore. So, no additional uncertainty you need to introduce while measuring from the pressure calibrator. Practically, the equipment for pressure calibration can be uncertain sometimes, whose consideration must be mentioned in your budget.

• Connection with the device for testing:  For connecting with the pressure calibrator, isolation of the pressure transmitter is under the testing process for pressurizing the small volume. Mainly, there are 2-ways or 3-ways valves present during the installation of the pressure transmitter. So, you can remove it from testing or connection with the pressure calibrator.

• Measurement of 4-20mA output: To measure the output signal of the pressure transmitter, you need to break the current loop for measuring the 4-20mA by using your meter or disconnecting the pressure transmitter completely. The current meter must supply the power to the pressure transmitter.

• Stability in the accuracy of the calibrator: it is the fact that there is no perfect stability in any pressure transmitter. Almost all the manufacturers provide the statement for stability and accuracy. You can combine both of these figures the determine the period of re-calibrating. The performance of every instrument is different from the other, so the time for the re-calibration also changes. There is a possibility to widen this time if you receive accurate results from the pressure calibrator.

• Generation of testing pressure:  One more important consideration is generating the forces. You can use pneumatic calibration as the source for the hand pumps for generating the pumps approximately to 40 bar. It is not easy to receive the maximum pressure rating that the manufacturer gives you. To create the pressure calibration from the hydraulic pump is more than 40 bar. For setting the pressures, the volume adjuster must be with the hand pump of the calibration. It helps in developing the point for the calibration in a single direction. So, there is no pressure during the calibration. Some of the pressure calibrators are available with hand pumps and volume adjusters. These are very easy to use while changing the range of the pressure.

• Accuracy in the calibration:  Overall, the accuracy of the pressure calibration must be the part of the meter you are using. You must investigate the error received from the temperature of both the meter and pressure transmitter. Although, the manufacturers mention the temperature range of the pressure calibrator. The examination is critical to make the statement for the accuracy on the datasheet when compared with other pressure calibrators.

What is the procedure for differential pressure transmitter calibration?

 

Tools you need are:

• The power supply of 24V DC
• Digital multimeter
• Pneumatic hand pump (approximately to 600 PSIG)
• Hydraulic hand pump (approximately to 10000 PSIG)
• Screwdriver toolkit
• HART communicator
• Low-pressure hand pump
• High accuracy digital testing gauge

Procedure for the calibration:

• I am setting the differential pressure transmitter, power supply, HART communicator, and multimeter according to figure 3.
• Do check the manifold of the equalizing valve is close
• You need to apply the pressure equal to the pressure of the lower range. It mostly corresponds to the 4mA in the output of the transmitter.
• Start reading the pressure on the LCD of the transmitter or HART communicator. You can do the adjusts with the HART communicator if there are any. So the output displays on the transmitter’s LCD and remains the same along with the applying pressure.
• With the help of a multimeter, read the mA output of the transmitter. After adjusting the HART communicator, make sure that the readings on the transmitter are 4mA.
• Keep applying the pressure equal to the upper range of the pressure. It corresponds to the 20mA in the transmitter’s output most of the time.
• Now again, read the pressure on the LCD of the transmitter or HART communicator.
• Read the mA output as well through the multimeter. Production on the transmitter is 20mA after the adjustments from the HART communicator.

What is the pressure transmitter calibration at the bench?

 

The technicians perform pressure transmitter calibration at the bench to ensure that the calibration is effective and doesn’t decrease the performance. They also check that all the components are working accurately after the installation. Evaluating every element is possible if there is any suspicion regarding the failure. The bench facilitates a specific environment for the calibration. It is a sort of opportunity for using the correct equipment and protecting from the conditions of the factory while testing the commission and calibrating the pressure transmitter.

 

For performing the test:

• Connect the transmitter testing hose from the calibrator with the transmitter
• Connection of the mA measurement jacks of the calibrator is with the transmitter
• You need to do the setting of the pressure selecting knob for the essential functions
• Apply the pressure from the pump from holding the “PUMP” button and release it when you have reached the pressure you need.
• Correct the values of the pressure through adjustment of pressure
• Study the pressure for the reference and output current you are receiving from the transmitter as the display
• Keep repeating all the testing points. If you find the measuring signal of mA at the testing points is in the tolerance, it means the test is complete. Otherwise, you need to make the adjustments.

What are the conditions for pressure transmitter calibration, and how often do you need to do it?

The pressure transmitters in the industries need to be durable and reliable for the processes. But still, they need calibration and maintenance to increase the performance. Therefore, you need to determine proper intervals for the calibration of every processing plant. It depends on the history and requirements of the process. For deciding the pressure transmitter calibration and follow the below conditions:

• What kind of regulations do you need to observe? (it can be safety, national, local, or environmental)
• What is the reason behind the pressure transmitter calibration? It can be for improving quality, maintenance or safety)

Conditions according to the process:

• Is there any homogenous processing fluid and pressure or temperature stability?
• Are there fluctuations in the conditions of the process?
• Can there be any risk of building up or corrosion in the pressure transmitter?
• Is there a chance of the presence of heavy vibration?

Ambient conditions:

Can you install the pressure transmitter in a completely controlled environment, the stability in the temperatures, low humidity, and some contaminations, including dirt and dust?

• Is there any possibility of exposing the transmitter to different weather conditions or high-level of humidity?

If there is no history or regulating requirements for the guidance regarding the pressure transmitter calibration, go through the below guidelines:

• When Direct mounting the pressure transmitter and installation the control environment on the process. It would help if you had pressure transmitter calibration every four to six years.
• When Direct mounting the pressure transmitter and installation outside the processes and stable conditions. The pressure transmitter calibration is dependent on the ambient conditions.

Figure 3 procedure for differential pressure transmitter

What is the formula for pressure transmitter calibration?

 

You can easily use a formula to convert most units using the 4mA or 20mA signals to the mA units. There are many other formulas, but below is the simplest one. It is the formula for converting the pressure to the current:

mA value= display value of the pressure/full range 16+4

if the value or range doesn’t begin with the zero (along with the range for vacuum), you can use the following interpolation formula:

X={(x2-x1) (Y-y1)/(y2-y1)} +x1

For encoding, you can even use the following excel for helpful conversions:

Unit	mA	Unit	Pressure
X=	12.0000	Y=	5.000
X1=	4.0000	Y1=	0.0000
X2=	20.0000	Y2=	10.0000

You can even calculate the error if you are willing to know it. Use this formula for calculating the error:

Error= measuring value- actual value

What is the Calibration Span?

 

Whenever you purchase a pressure transmitter, you have the range for the instrument that includes the pressure range supporting the device. Overpressure range is also available that can happen in the instrument. There are particular values in the measuring range where the transmitter works properly and ignores the overpressure. The upper limit and lower limit are the definitions of the range. A calibration span in the measuring range also shows the device’s ability to work according to the application. The calibration span is the difference between the upper and lower range values you read on the transmitter. You must know the calibration span of every instrument it can support. The readings are inaccurate whenever you are above or below the limits.

 

Who performs the pressure transmitter calibration?

 

Instruthinkhas highly-trained technicians for pressure transmitter calibration. They thoroughly qualify for documenting and maintaining the calibration process. Repetition is the primary key in calibration, so we need to do documentation to make it happen. The accurate cycle for the pressure transmitter calibration depends on the calibration and application. You can easily employ the pressure transmitter in various operations or processes. It needs different intervals in the calibration. These calibration practices help save costs during maintenance and deliver high performance. Always document the results of the calibration and follow the proper procedures.

 

What are the cautions for handling the pressure transmitter calibration?

 

Step	Task	Details of the task
1	Unpacking	Unpacking the packing of the transmitter
2	Checking the model and specifications of the pressure transmitter	Check the delivery transmitter is similar to the options provided in the template
3	Storage	● There is no exposure to the water and non-vibrating. ● Suitable temperature 25 degrees Celsius and relative humidity is 65%
4	Bench for the calibration	Configuring the range, zero spans, transferring function, tags, and different parameters.
5	Location of the installation	● Where there are no fluctuations in the suitable temperature. ● No corrosions in the chemical materials ● No severe impact or any vibration ● Easy to maintain
6	Mechanically considerations	● It is where you can handle the transmitter without any difficulty ● Be careful regarding the leakages of the pressure
7	Considering electrically	● Connecting with the 24V DC supply ● The resistance range must be from 250 ohm-550 ohm during the HART communication.
8	Mounting and installation	● Mount the transmitter with a suitable bracket. ● The transmitter must be firmly fixed with its frame.
9	Calibration on the target	● During the start-up and structure of the transmitter, sensor zero trim is recommended. While the zero trimming, there is an establishment of the zero baselines of the transmitter. ●  Before the initiation of the zero trim, the PV value of the transmitter needs to be zero, and the output for the current is 4mA.
10	Pressure	● There is no need to apply the full lining and differential pressure suddenly. ● You need to close the equalizing valve that 3/5 portion of the manifold. Later, gradually open and stop the valve on the high and low sides.
11	Working of the transmitter	● Check that the transmitter is working according to the specifications.

What are the troubleshooting issues during the pressure transmitter calibration?

 

Reason	Source of the reason	Solution
No communication of the pressure transmitter with the HART communicator	Wiring in the loops	● The minimum resistance must be 250 ohms between the supplying power and the HART communicator. ● Always check the open circuits and different grounds.
Receiving the higher output	● Failure in the sensor input ● Power supply ● Loops in the wiring ● Module for the electronics	● Connection with the HART communicator and go in the testing mode of the transmitter to isolate the sensor’s failure. ● Note down the output voltage receiving at the terminals of the transmitter. The range has to be between 11.9 to 45V DC supply.
Receiving no or low output	● Element for the sensor ● Loops ● Modules for the electronics	● Check the polarity of the signal terminal ● Make sure that the limits of the sensor are in the range of the sensor.

What are the intervals for pressure transmitter calibration?

Mainly the industrial applications schedule the calibration every year. The intervals for the calibration can be for three months for those industries where critical situations arise. It includes applications of the pharmaceutical and manufacturing regarding medicine applications. During the pressure transmitter calibration, the technical team places the date for the calibration verification when the pressure transmitter is in service. There is a recording for the transmitter output in the calibration whenever you apply the pressure at the five points: zero, 50% full scaling, 100%, repetition again at 50%, and then zero. You can control and adjust the spans of the pressure transmitter. It is essential to receive accurate calibration in the particular tolerances. You can now record the data and document it. The pressure transmitter returns to the service again. This calibration process is earlier than the shipment of the pressure transmitter.

 

Final thoughts:

The pressure transmitter by the Instruthinkis the superior product that our factory designs and manufactures. Instruthinkis the right choice if you are looking for a reliable pressure transmitter. It is available at an economical price, depending on your project. You can take guidance and assistance from our professional team members regarding the pressure transmitter calibration. 100% technical support is available regarding the supply of the pressure transmitter. Email us now without any delay and tell us your requirements.