2 replies to this topic

[deltaChe]

How could process engineers set up an appropriate span range for the LT transmitter
if I know the HH Alarm and LL Alarm from alarm list?
Is the lowest transmitter tap is the LL alarm point and highest transmitter tap is the HH alram point?
For example, there is a vessel tan-to-tan is 48", how can I find out the maxiumm transmitter span
if we know the alarms is set to be at 10% and 90% span?

Thank you very much for your help.

[fallah]

How could process engineers set up an appropriate span range for the LT transmitter
if I know the HH Alarm and LL Alarm from alarm list?
if we know the alarms is set to be at 10% and 90% span?

All depends on what is considered in the relevant project specifications.

10% and 90% of the "tan to tan" length,if would cover HH/LL alarms,can be considered as LT span.

[Himanshu Sharma]

Sir,

LT span means u want to read the entire value of level with in that range.From Process point of view ,you should be able to read between Low Low Level and High High Level or Low Level and High Level for that matter.

Low alarms is provided a bit Above the Process Low Level and High Alarm is provided a bit lower than Process High Level.

I just could not get your point of Tan-Tan Length !!!
if you need a simple method try this,Subtract Low Level vessel Mark from High level .Add 10% of it to your Low Liquid Level for Low alarm reading and 90% of it can be your high alarm reading.

Having said that ,i would like you to ponder over the fact that alarms are meant for Human intervention and there must be sufficient time to do so.for very small vessels providing LAL/LAH values are of no use because there is no time for action and setting them a bit high means the alarms will bother you a lot even during normal operation with minor fluctuations.

Hope That Helps !