Previous in Forum: Honda Civic - Ignition Kill and Lo-Jack   Next in Forum: Regarding Gap voltage for VIbration probe
Close
Close
Close
5 comments
Rate Comments: Nested
Participant

Join Date: Dec 2008
Posts: 1

Replacing a Level Transmitter

12/16/2008 3:37 AM

I want to ask, how to replace a level Transmitter (DP open System) by another type due to process density instability.

a- what factors should be considered?

b- what type you would use?

c- How you are going to implement the replacement

Mention all related safety actions to be done during execution process?

Register to Reply
Pathfinder Tags: DP open System
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Guru
Philippines - Member - New Member Engineering Fields - Instrumentation Engineering - New Member Engineering Fields - Control Engineering - Who am I?

Join Date: Oct 2006
Location: Northern Mindanao, Philippines
Posts: 2147
Good Answers: 53
#1

Re: DP open System

12/16/2008 5:15 AM

What issues are you having with unstable process density? It might have some bearing on what our answers will be.

However, just to give an immediate answer, I would use load cells (weight measurement). I've had problems with differential pressure transmitters (product sticking to the diaphragms) so I shifted to load cells.

regards,

Vulcan

__________________
Miscommunication: when what people heard you say differs from what you said. Make yourself understood.
Register to Reply
Power-User
South Africa - Member -

Join Date: Nov 2008
Location: Johannesburg
Posts: 295
Good Answers: 12
#2

Re: Replacing a Level Transmitter

12/17/2008 12:39 AM

Hi there,

You are going to have to provide a bit more data. You say it is an open system, but you have problems with changing density. Is the medium single or multi phase? Do you have agitation in the vessel? What is the process medium and what are it's chemical properties?

All these and more will determine your choice of measurement type selection.

Load cell is definately very good - but expensive if your vessel is huge.

Try to provide a bit more chemical and mechanical data and you will get a better answer. No instrument engineer will commit to a definate answer with the data you have provided as it is impossible to answer any single one of your questions.

Regards

Craig

Register to Reply
Active Contributor

Join Date: Jun 2007
Posts: 18
Good Answers: 1
#3

Re: Replacing a Level Transmitter

12/17/2008 7:43 AM

If changing densities are the issue then obviously weight is variable so load cells won't help you determine the volume (liquid level) in your application. You need to provide alot more specifics for a rational answer....

- density variations (specific materials) and other material specifics

- foaming?

- vessel (tank) size

- location

- available or retrofitable nozzles

- remote indication?

- etc....can't supply "too much" info.

Register to Reply
Guru
Philippines - Member - New Member Engineering Fields - Instrumentation Engineering - New Member Engineering Fields - Control Engineering - Who am I?

Join Date: Oct 2006
Location: Northern Mindanao, Philippines
Posts: 2147
Good Answers: 53
#4
In reply to #3

Re: Replacing a Level Transmitter

12/17/2008 8:07 AM

If changing densities are the issue then obviously weight is variable so load cells won't help you determine the volume (liquid level) in your application. You need to provide alot more specifics for a rational answer....

I agree. I just provided the load cell solution as a suggestion since that's what I used. We're not really concerned with having an accurate indication of level. We're more concerned with preventing product from overflowing. To address that, we calibrate the tank using the lowest density solution we will be putting in the tank (water actually). That way, when a product with higher density is put into the tank, the level at 100% indication is actually lower.

If we wanted to, we could put a density meter in the tank so that we can compensate for it. However, as I said, we're not concerned with that.

The added benefit of using load cells was reliable level indication. With differential pressure transmitters, we had problems with product sticking to the diaphragms and preventing them from indicating the level correctly.

regards,

Vulcan

__________________
Miscommunication: when what people heard you say differs from what you said. Make yourself understood.
Register to Reply
Guru

Join Date: Aug 2007
Location: Indiana, USA
Posts: 579
Good Answers: 61
#5

Re: Replacing a Level Transmitter

12/17/2008 8:43 AM

a- Primary factors include the environmental conditions for the transmitter (temperature/pressure/chemical/other) and density extremes of the material (as the material separates, what is the maximum density? minimum density?). You should also consider how much churning or wave action there is at the point of measurement, which would determine if you need any type of measurement delay time or dead band. The precision and accuracy requirements for the measurement will also help determine the type of system you need.

b- I would seriously consider using a float system. You can get them for just about any type of liquid. I have used them in sumps, acid tanks, mixing vats, and many other situations. Select a sensor which will float on top of the lightest density extreme of the process material. For example, if you have a mixed liquid, take a sample and let it sit until it stratifies. Draw off the lightest fluid (the top layer) and measure the density/specific gravity. Select a float with a density about 5-10% less than the measured sample.

c- Talk to an application engineer at the float manufacturer. I sometimes talk to 2 or 3 different companies. It gives me a better understanding of all the options, as people tend to downplay the limitations of their own product, and emphasize any weaknesses in their competitor's system.

Implementation planning, including safety aspects, cannot be accomplished without detailed information on the process material, process system, and physical arrangement.

__________________
Experience: The knowledge you gain just AFTER you needed it.
Register to Reply
Register to Reply 5 comments
Copy to Clipboard

Users who posted comments:

craigza (1); Pete (Contol Systems) (1); pwr2thepeople (1); Vulcan (2)

Previous in Forum: Honda Civic - Ignition Kill and Lo-Jack   Next in Forum: Regarding Gap voltage for VIbration probe

Advertisement