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Process Calibration Tools Frequently Asked Questions


Q

Just what can you do with HART smart devices with the Fluke-744?

A

The Fluke 744 can perform calibration on many HART devices and download the results for storage. The 744 can program a variety of attributes in a transmitter but not all . It will not replace a HART communicator for all hart devices to perform all HART tasks. It will not store the configuration of the transmitter to upload to a computer. It will capture the devices performance via a performance test and will capture the transmitter tag number, serial number and ranging.

The 744 can program the tag number, measurement units, range, dampening and transfer functions. It can adjust most if not all mA outputs of transmitters, command a transmitter to perform a loop test and perform the pressure zero adjustment of pressure transmitters as these are universal commands.

For the devices we support we can perform sensor trim on the inputs of temperature and pressure transmitters and configure the sensor type for temperature transmitters. For supported multivariable transmitters we can map the variable and configure the dual sensor configuration (setting a dual input temperature for hot back up for example).

The 744 can do light programming and configuration and is intended to replace the need to carry a communicator to the field for calibration. Some users find its capabilities eliminate the need to take a communicator to the field except for non-supported devices such as valves or other complicated devices that require a laptop or communicator.

The HART calibration application note “HART Transmitter Calibration”, has the HART list of available commands, list of supported devices and example of how to use the 744 to calibrate both a HART temperature and pressure transmitter.

Q

What are some of the costs and challenges of moving from a paper-based instrument calibration system to digital record keeping?

A

Often acquisition costs are the smallest challenge in setting up digital record keeping. Documenting Process Calibrators (DPC's) being multifunction devices are the premium priced field calibrators ranging from $5K-10K. That said, they are usually multifunction giving them a wide workload coverage and they often have other useful features such as HART configuration capabilities or the ability to log measurements for trending. Even if the documenting aspect of these calibrators is not used, these DPC's replace the need for a bucket full of tools. Calibration Management Software (CMS) pricing varies greatly. Single user entry level products range from $2K, but more comprehensive networked versions with sophisticated predictive maintenance capabilities and workload management can cost as much as $100K or more. The more of the software you use, the better value on your return.

The critical element to succeeding in setting a digital record keeping system goes beyond the decision to commit funds to a purchase. The purchase needs to be accompanied by an additional commitment from maintenance management to staff if it is to succeed. Up front, this means assigning a super user that is the key operator/administrator of the system. There is a lot of initial work getting all of the instrument tags into the CMS.

This can often be done via ASCII import of the existing tag information if there are any kind of electronic records that describe them. Critical information includes (but not limited to) tag number, serial number, input span, required accuracy, and test procedures. Once the initial information is entered, there is follow on maintenance refining the tag information, adding new tags, and maintaining test equipment record for traceability purposes.

Q

What are the advantages of calibration management software over paper- bases systems?

A

While the challenges and costs seem daunting, the reward, once a DPC/CMS system is in play is huge. It is easier to predict staffing requirements over periods of time. Doing predictive maintenance of critical tags is enabled through advanced analysis tools such as drift plot analysis. These tools allow the system owner to use As-Found calibration data to do calibration interval adjustments or determine if the maintenance cost of a device is such that its' replacement is justified.

In the event of an audit by a quality organization or regulatory agency, access to critical calibration records for suspect instruments is at the fingertips of the process owner. No concerns of legibility or finding a specific piece of paper. Most CMS packages have flexible search tools for finding tags sorted in a variety of ways. For example, find all the pressure instrument tags in a process unit to send a technician out to perform calibrations.

One of the main benefits is the interaction of the procedures loaded into the DPC from the CMS software. Once the procedure for an instrument is loaded into the DPC, the user selects the pre-configured procedure for the tag. Many DPC's can give the user connection information or walk the technician through an isolation procedure or lock-out/tag-out procedure. Once connected, the DPC will be automatically preconfigured correctly for test. The inputs to the tag are known, the expected measured output is known as the expected tolerance. With that information, the DPC can determine pass/fail while logging the As-Found calibration results. In the event of a failure, many DPC's can guid the user through the adjustment process. Once adjustment is completed, the calibration performance test can be repeated and the As-Left calibration results are recorded. This information is recorded into the DPC memory for alter upload into the CMS, after which the results can be reviewed and/or printed. There are no issues with legibility of test records or transcription errors. Results cannot be falsified and the DPC's can be reviewed prior to upload to ensure that the procedures downloaded from the CMS were used. With a system such as this, the integrity of the data is both insured and protected.

Q

How do I change the mA range on my Fluke Process Calibrator/Meter to 0-20mA or 4-20mA?

A

Fluke 705 - Press and hold the up arrow button (▲) on power up until the new mA zero value appears on the display. Repeat to change back.

Fluke 707 & 707Ex - Press the “MODE” button on power up, you can release the buttons after unit powers up.

Fluke 715 – Select the “Output” zero value and press and hold both up arrow buttons simultaneously (▲▲) to store and repeat for the span value.

Fluke 787 – Press and hold the “RANGE” button on power up.

Fluke 789 – Press and hold the “RANGE” button on power up.

Fluke 725, 725Ex, 726 – In the Output mode select the desired zero value and press and hold the “0%” button for ~3 seconds. To set the span, select the desired value and press and hold the “100%” button for ~3 seconds.

Fluke 772 & 773 – Press the shift button to activate ▲, ▼, ◄, and ► to adjust the source output. Long press the 0% or 100% button until the percent value changes to either 0.0% for zero or 100.0% for span.

Q

How do I select a Fluke pressure module for my application?

A

“Differential” pressure modules have two pressure ports, a High and Low side. The High side is signified by the capital letter “H” and the low side by a capital “L”. When working with a differential measurement, most devices (like a differential pressure transmitter) will also have a “H” and “L” port. The “H” side of the module will be connected to the “H” side of the UUT (Unit Under Test) and the “L” sides connected together, thus seeing the same input values and the measurement reading will be the difference in pressure between the “H” and “L” ports. If, for example, you are calibrating a pressure transmitter that’s low side is set to zero, then you can leave the “L” side of both the pressure module and UUT vented to atmosphere.

“Dual” pressure modules will read both positive and negative pressures through a single input port.

“Gauge” pressure modules read pressure relative to the local atmospheric or ambient pressure, also known as one atmosphere. It’s stated in units of “G” (Gauge), for example if you are measuring PSI (Pounds per Square Inch), the pressure will be listed as PSIG.

“Absolute” pressure module measurements are referenced to zero pressure absolute or a perfect vacuum (-14.7 PSIG or 0 PSIA). When these modules are open to atmosphere they will read approximately 14.7 PSIA (~1 atmosphere at sea level), except for the 700PA3 that will only read as high as ~5.5PSIA. With absolute pressure starting at a true zero, there cannot be a negative absolute pressure measurement.

“Vacuum” pressure modules read only negative pressure with atmospheric pressure being your reference.

“High” pressure modules have three ranges: 3000, 5000 & 10000 PSIG.

Note: If performing work with Fluke Pressure calibration modules and mainframes, we recommend that a Fluke 700ILF (In Line Filter) is used for clean dry air or nitrogen work. The 700ILF burst pressure is 500psi.

Q

What is the difference between “Source” and “Simulate”?

A

Source will actually output a 4mA to 20mA signal based on the value selected. Simulate does not output anything but rather controls the current flow from an external source to be within 4mA to 20mA.

Q

When simulating an RTD to the input of a RTD transmitter, why don’t I get the proper readings?

A

Beside making the proper 2, 3 or 4-wire connections (see above question), the RTD transmitter must be outputting the proper excitation current into the calibrator. Check the calibrator’s excitation current spec’s for RTD sourcing. Also, some systems apply the excitation current as a pulse, not continuously. The calibrator excitation pulse spec’s must be checked, if available. The 744 can handle pulses as fast a 1msec. Some calibrators cannot work that fast and some are not even specified to handle pulses.

Q

What can I do if my HART transmitter is not fully compatible with my 744?

A

See example 3 that starts on page 10 of the application note “HART Transmitter Calibration”.

Q

How do I calibrate a HART transmitter with the 744?

A

See examples 1 and 2 (pages 6 and 8) in the application note “HART Transmitter Calibration” for detail step-by-step examples.

Q

How to I get a list of the HART transmitters that are totally compatible with the 744?

A

See page 5 of the application note “HART Transmitter Calibration” for a list or see the 744’s feature page on our web site.

Q

My “NEW” Fluke 744 (or 741B or 743B) keeps asking me for a registration code?

A

Go to that product page at www.Fluke.com and register the product (register 744, register 741B, register 743B). When you received the code (it may take up to three weeks) then enter it into the calibrator. Procedures are included with the returned code. This will unlock the “Transmitter Mode” and “Bar Code Scanner” functionality of the calibrator. (743B & 744) Transmitter mode allows the user the ability to temporarily use the calibrator to substitute it for a defective or suspect transmitter. The calibrator will continue to ask for the code once-a-day for the first 30 days. See next question.

Q

My “two year old or older” 744 (or 741B or 743B) is asking me for the registration code?

A

The internal memory battery has expired and the calibrator can’t remember anything that’s manually entered after the power is turned off. The part number for the battery is 929369 which is a 3 volt Lithium CR2032 watch type battery which hides under the LCD display. Opening the calibrator will probably break the calibration seal so it will probably need recalibration, so having the Fluke repair department replace the battery and recalibrate the calibration might a better choice than the user changing the battery themselves. Cal labs should replace the memory battery every other year at recalibration time.

Q

How do I connect my 743B (or 741B) to source (simulate) to a 3 or 4-wire RTD transmitter?

A

The user manual is missing a hookup diagram. See figure 21 on page 58 of the 744 user manual or download the application note called “Transmitter Calibration with the Fluke 700 Series Documenting Process Calibrator” and see the diagram on page 5 of 15. This applies to all of our Process Calibrators. They will all measure 2, 3 or 4-wire RTD’s but they only source as a two terminal device. The idea is that the jumper cables that come with the calibrator allows for making 3 or 4-wire connections from the calibrators 2 terminal source terminals.

Q

My 744 (or 741B or 743B) when sourcing 4mA to 20mA says “Compliance Voltage Exceeds Limits”. Why?

A

The input resistance of the UUT (typically a transmitter) being fed the current is above 1200 ohms or the test leads or another part of the circuit are open. (24V maximum compliance voltage divided by 20mA = 1200 ohms) For testing purposes, just short the test leads together to see if the message goes away.

Q

My 744 (or 741B or 743B) when simulating 4mA to 20mA says “Open Circuit Detected”. Why?

A

The calibrator is not detecting a current between 4mA and 20mA that it can control. An open test lead is one cause. The other popular one is that a 24V loop supply has not been put in the current loop.

Q

What is the model number of the cable that connects the 744 and the Hart Scientifics dry wells?

A

Hart Drywell Cable is Fluke item #2111088.

Q

How do I check a limit (pressure, temperature, etc) switch with a 740 Process Calibrator?

A

See the application note titled “Limit Switches and Limit Switch Applications with the 740 Series DPCs”.

Q

My 789 (or 787) mA output show’s dashed lines (- - - -)……Why?

A

The input resistance of the of the transmitter being fed the current is above 600 ohms for the 787 or 1200 ohms for the 789, the fuses are blown or the test leads or another part of the circuit are open. For testing purposes, just short the test leads together to see if the flashing - - - - goes away. Be sure that the user is using the correct jacks marked in orange color (output mode colors), not the white colors (measuring mode colors).

Q

My 789 (or 787) when simulating 4mA to 20mA the display shows dashed lines ( - - - -)…..Why?

A

The meter is not detecting a current between 4mA and 20mA that it can control. Blown fuses or an open test lead are some of the causes. The other popular one is that a 24V loop supply has not been put in the current loop.

Q

My 725 (or 726) when sourcing 4mA to 20mA flashes OL. Why?

A

The input resistance of the transmitter being fed the current is above 1200 ohms or the test leads or another part of the circuit are open. (24V maximum compliance voltage divided by 20mA = 1200 ohms) For testing purposes, just short the test leads together to see if the message goes away. Note that the 724 does not source 4mA to 20mA.

Q

My 725 (or 726) when simulating 4mA to 20mA flashes OL. Why?

A

The calibrator is not detecting a current between 4mA and 20mA that it can control. An open test lead is one cause. The other popular one is that a 24V loop supply has not been put in the current loop.

Q

My 707 (or 705 or 715) when sourcing 4mA to 20mA flashes OL. Why?

A

The input resistance of the of the transmitter being fed the current is above 1200 ohms or the test leads or another part of the circuit are open. (24V maximum compliance voltage divided by 20mA = 1200 ohms) For testing purposes, just short the test leads together to see if the message goes away.

Q

My 707 (or 705 or 715) when simulating 4mA to 20mA flashes OL. Why?

A

The calibrator is not detecting a current between 4mA and 20mA that it can control. An open test lead is one cause. The other popular one is that a 24V loop supply has not been put in the current loop.
        
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