We had selected English language on the displays of our Magnetic Flowmeters. But 17 Nos of displays started showing arbitrary characters (non English language characters, symbols etc.) on their displays. Water Flow digits shown on displays were correct. Even the 4-20mAmps signal interfaced with the Siemens S7 PLC was OK.
Display Card Part No.: 08732-0006-E001
Magnetic flowmeter Model N0.: 8732EST2A1NAM4
Make: Rosemount
After replacing the faulty display cards with new healthy ones, problem was resolved. We have faced this problem in 17 Nos flowmeter displays in last 3 years. Can anybody help me to solve this problem?
There are a few possible causes for the 8732E displays showing arbitrary characters.
1) Unclean or insufficient power including power spikes. These can disrupt the RAM of the display so that it uses random symbols for display characters.
2) Poor connection to the electronics board. This can cause issue #1.
3) Electrical noise generated from an external source. This can cause issue #1.
4) Faulty display.
To troubleshoot the situation, you should begin by cycling power to the device. If cycling power clears the arbritrary characters it is most likely caused by a temporary power disruption or noise issue that is corrupting the display's RAM. Care should be taken to provide clean and stable power to the device. Look for other nearby sources of possible electrical, RF, or magnetic noise that could also contribute to issues with electronic equipment. Next make sure the connection pins between the electronics and display are seated properly and making a good connection. If the arbitrary characters persist then the display should be replaced. Further detail on installing a display and maintenance can be found in the Reference Manual using the following link - www2.emersonprocess.com/.../00809-0100-4662.pdf.
In reply to Mike Schaefer:
Hi all,
run into same kind of problem last fall.
The problem was that the customer added a VFD to a pump motor from keeping it from cavitating.
They used unshielded "Ground-cable" to connect the motor to the VFD.
The supply lines and signal lines were running side by side with the VFD, also the motor was only 1 m away from the MiMo.
The problem was solved by adding more grounding to the transmitter and move the signal cables a little bit
Niklas Flykt
Klinkmann Oy
Key Account Manager safety products
nikfly@gmail.com
In reply to Niklas Flykt:
Hi,
When the use of VFD:s is encreasing more and more in almost all areas for control, it is more and more import to take notice of the cabling and requiered EMC filter/protectings to avoid disturbance to other ecuipments.
To use a VFD:s saves energy in every application were the motor is not supposed to run at full speed all the time. In my personnal oppinion to use flow valves to decrease flow is not the right way to go if you only have one flow
that you wan´t to control... It´s like you start driving your car in full speed and regulate the speed by pressing the break.
VFD:s are cheap at the moment, if you use a VFD you get the full motor surveillance at the same time, you do not need to install any other monitoring equipment and the newest one are equipped with safety built in, that will aslo save contactors and safety logics and cabinet space. When you use VFD:s you do not have to design complex control circuits in the cabinet just add the feed and the control cable or fieldbus.
But when you use them you have to take inconsideration that you should choose the motor and cabling according to manufacturers reccomendations. You will get problems by not using properly shielded cables to the motors or leaving out the EMC filters on the supply side to the VFD (the thyristor bridge on the supply side will cause disturbance on the feeding side).
I found an intresting article about the effect of different cables: http://www.automation.com/library/articles-white-papers/motor-drives-control/factors-to-consider-in-cabling-a-reliable-vfd-system
"As demonstrated by its trace in that figure, foil shields are simply not robust enough to capture the volume of noise generated by VFDs. Unshielded cables connected between a VFD and a motor can radiate noise in excess of 80V to unshielded communication wires/cables, and in excess of 10V to shielded instrumentation cables. Moreover, the use of unshielded cables in conduits should be limited, as the conduit is an uncontrolled path to ground for the noise it captures."
Also you should also not put the motor cables on the same cable shelves as the control/communication cables.
here is a longer PDFon the same subject: http://www.concables.cl/catalogos_pdf/info-tecnica/belden/cables-para-aplicaciones-pwm-ac-vfd.pdf
These kind of "Ghost" voltages/disturbances are really hard to track down an takes a lot of time and money. It´s better to do the things right the first time so you don´t end up putting RFI filters in thousends of inputs afterwards
Thanks for your very thorough response, Niklas.
Best Regards,
Rachelle McWright: Business Development Manager, Dynamic Simulation: U.S. Gulf Coast