Flow for safety!

One series Flow transmitter for safety

1XTXSW-K10 – A smart with HART 7 DP transmitter/switch for measuring and controlling the flow. Alternatively, it is used as a wiHART DP transmitter with localized flow control.

2SLPxx-K10 – A SIL 2 certified SIL 3 capable DP transmitter/switch for measuring and controlling the flow.

Application case study (All the characters are imaginary):?

Refinery Team involved:

·?????? Yul Brynner – Site President

·?????? Charles Bronson – Central Engineering Services Head

·?????? James Coburn – Instrumentation Head

·?????? Eli Wallach – Head of procurement

·?????? Steve McQueen – Head of finance.

·?????? Parry Joshi – A Salesman from United Electric Controls

Being responsible for Instrumentation maintenance, James had a tricky situation. There was a limited budget on hand and Charles wanted to increase the reliability and minimize the maintenance budget. Yul had set a clear vision in his weekly meeting that, if there is an innovative and out-of-the-box solution, he is ready to go for it. Eli Wallach didn’t have much width in his budget so he was focused on any solution that saved the budget, no matter it came from a vendor not listed on their AVL.

James had some challenges in flow measuring. There were many locations in the plant and varieties of fluids, line sizes, static pressure, and temperatures. Because flow measurement was required with control for safety, most of these applications did not require precise measurement. James had a task on hand, he wanted a technology that was familiar to every plant technician at all levels, be it junior or senior and there was no need for training. Besides, it was necessary that the hooters blow and beacons started flashing if the flow dropped below a certain flow rate or increased more than required. All these needed additional hardware, man-hours, and programming in the control room, and per Charles, Eli had a tight purse and Eli didn’t want to go to Steve McQueen for approval of extra finance. Yul, however willing to approve the extra budget but it was possible only by splitting it with the provisional budget for the next year. Meanwhile, the boiler had a trip recently because the low flow went undetected with a faulty mechanical flow switch. This resulted in production loss and everyone in the headquarters wanted a detailed RCA (route cause analysis) report. Yul had a deadline to meet.

Amid all this, a salesman named Parry Joshi called from United Electric Controls asking for time to make a presentation on a DP transmitter with unique features. James and Charles were preparing for plant shutdown in April 2024 and they were holding extensive meetings with Eli for their PR (purchase requisitions) approvals for their upcoming plant shutdown. They had a limited window of 20 days of plant shutdown in which, most of the instrumentation needed to be modified, upgraded, or replaced. Hesitantly, Charles and James agreed to meet Parry even in their busy plant shutdown preparations, because United Electric, the company Parry worked for, had a strong reputation of having unique solutions, that no other manufacturer could offer. Considering UE’s reputation, Charles and James thought that they could share a few process problems with Parry.

Charles and James’s team members filled the conference room. Charles told Parry “You have 20 minutes!” and then they had to go for a meeting with Yul and Eli.

Parry thanked saying, “Your 20 minutes could save hundreds of hours and thousands of dollars in your plant maintenance!”

As Parry started to speak on One series model 1XTXSW with differential pressure for flow transmitter, everyone in the room was amused “What was new in this? It is just an ordinary DP transmitter!”. As Parry moved forward his slides showing that 1XTXSW had two solid state relays inside, Charles and James realized that 1XTXSW with field control capability was something they didn’t find from any DP transmitter manufacturer! It means they didn’t need to buy a flow switch! Charles looked at James and asked “Should we ask UE to supply orifice?” to which James said, “No, they are sourcing orifices from a reliable supplier named John Travolta”. James said, all his team members including Tom and Harry were finding flow switches a big headache. Most flow switches like paddle or plug type had an error margin of +/-10% of the flow, they were not reliable and often resulted in false alarms/trips. The thermal flow switches needed an external power supply and they were quite expensive considering only the purpose of switching. Yul could not agree to buy tens of expensive thermal flow switches only for control action. Besides, James had challenges of limited manpower and a short time for execution. Knowing that, some technicians are still isolating themselves if found covid positive, the challenge for James was to meet or beat the deadlines.

So with Parry mentioning that the 1XTXSW could serve the purpose of two flow switches, configurable set points, and dead bands sitting in the comfort of the control room, Tom raised his hand - for a question to Parry “Does 1XTXSW have square root output?”. Parry knew this question could come up anytime. “No! Your control system is better than the transmitter for the square root calculations” “It is better done in the DCS and not in the instrument”.

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The 1XTXSW-K10’s linear DP output is inversely proportional to the flow rate. Thus, the process engineer would be able to see the flow trending and compare the flow control in the field. There are a bunch of diagnostics from the unit itself including plug port detection. Parry went on to narrate many additional features of 1XTXSW it had trip counters, delayed switching, and most importantly, the DP transmitter was to be calibrated for Differential Pressure for both transmitting and switching. Above all, it did not need a flow lab!

“What about functional safety?” James asked as he was also responsible for reliability. Parry mentioned that One series has an SIL 2 certified and SIL 3 capable with a yellow enclosure marking a safety instrument, with the industry's best SFF. With this instrument, it serves the purpose of an independent flow shutdown system, it is a good package for remote locations.

Charles and James seemingly convinced had a meaningful look at each other. They decided to take Parry to Yul Bronson immediately after the presentation was done.?

Charles asked Parry “Would you repeat your presentation to our Site President, Yul Bronson again and explain to him these salient features?”

Eli was happy too after coming to know that one product solves the problem of hardware, maintenance, erection, and commissioning.

Steve McQueen would be the most happy person if the plant instrumentation was improved not just within its budget but by saving a huge sum. (He would recommend Yul to award special incentives to James and his team).

James asked Parry to send a specification datasheet so he could raise a PR.

For the academic interest of all, here is the principle of operation: Flow transmitter/switch.?

This application note explains only general DP flow measurement and control. This application note is not related to high-accuracy DP flow metering for custody transfer.

This application focuses on keeping the process flow in a safe range by the use of integral solid-state relays in the DP flow instrument.

·?DP transmitter/switch Model 1XTXSW-K10

·?An Orifice

Measuring flow with differential pressure is an almost 100-year-old technology and almost all instrument engineers in the industry are familiar with it. Practically for a wide range of liquids or liquids with solids or gases.

A differential pressure or ΔP transmitter measures the difference between high and low-pressure points.

To measure the flow using a differential pressure method, a restriction is placed in the flow line, often an orifice plate. The velocity of the fluid entering the orifice is lower than that of the fluid leaving the orifice. The increase in the velocity results in lower pressure. Thus, the pressure on the upstream side before the restriction is higher than the downstream side after the restriction. Such a reduction in pressure will cause an increase in the fluid velocity because the same amount of flow must take place before the restriction as after it. The velocity will vary directly with the flow and as the flow increases a greater pressure differential will occur across the restriction.

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·?????? The differential pressure is proportional to the square of the flow rate.?

·?????? Thus, the flow rate is directly proportional to the square root of differential pressure.?

UE’s One series model 1XTXSW-K10 is a smart HART 7 DP transmitter with a 4-20 mA output proportional to the differential pressure. For the DP transmitters with proportional output, the square root extraction is done in the control system to calculate and indicate the flow.

There are DP transmitters available with square root extraction output but it is recommended that square root extraction be done in the DCS because of its higher computational capability than the transmitter. There are incidents reported that an Instrument Engineer configured square root extraction output from the DP transmitter and the process engineer again applied square root extraction in the DCS. Then there are occasions when an Instrument Engineer didn’t configure the transmitter with square root extraction thinking that the process engineer would do it in the control system. On the other hand, the process engineer didn’t apply square root extraction in the control system assuming that the Instrument engineer might have already chosen square root extraction output from the transmitters itself. So considering the above possibility of the error, it is safer to have One series 1XTXSW-K10 with linear output so the square root extraction can be applied in the control system itself.

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In the case of One series 1XTXSW-K10, the local display will indicate a normal differential pressure across the orifice but the DCS which does square root extraction will indicate a flow rate.

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The restriction element (often not in the scope of a DP transmitter supplier), is an orifice. It is placed between the two flanges of the pipeline to create the restriction and differential pressure across the orifice.

The formula for calculating Square root output

Calibration method using linear output in an instrument lab:

An important point to note here is that the customer has to specify the DP range for the calibration and not the flow rate. UE doesn’t calculate the DP basis on the flow data because the responsibility lies with the orifice manufacturer. Assuming that, the customer has already this information, we will consider an example of the flow calculation in the DCS.

Advantages of 1XTSW-K10 DP flow transmitter with controls:

·?????? Very fast response time compared to conventional controls through PLC

·?????? Less time for engineering design

·?????? Less time in implementing the controls

·?????? Reduced time in design and configuration, testing, and hardware

·??????? Less time required in commissioning

Why is the orifice a restriction element for standard DP flow measurement?

·?????? Simple and inexpensive.

·?????? Used for liquid, steam, and gas.

·?????? Available in various sizes.

(Ensure 10D and 5D upstream and downstream straight run)

·?????? Practically any type of liquid flow is measured, even with some particles.

Typical applications:

1.????? Flow measurement and control for safety.

2.????? Burner Management systems – preventing over-firing of the furnace due to overflowing of the fuel to the furnace chamber with alarms high (alarm), and high-high (trip) to prevent the accumulation of unburned fuel in the furnace chamber.

3.????? Burner Management systems – fuel flow interruption alarms for low flow or low-low (trip)

4.????? Across the filter in a flow line, a popular application.

5.????? Prevents dry run of the pumps.

?One series considerations:

?·?????? The One series K-10 sensor will be good enough to meet most DP across the orifice in normal flow conditions.

·?????? No moving parts like paddle or plug-type switches, no false alarms, and no huge error margins. Long-term stability of the flow set points.