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Functional Test -mA Values to be Sent Using Communicator to Test SIF Function

03/13/2019 12:15 AM

i need to figure out the mA values to be sent using communicator to test a SIF Function.scenario as below:There are two flow transmitters with different instrument ranges(0-40MMCFD &0-130MMCFD) the total value of which is considered in the System for tripping. If the total value becomes less than say 6MMCFD,the trip function should initiate. For testing this, how much mA should the technician be sending using the communicator from Individual transmitter to show a value of 5.2MMCFD in system

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#1

Re: Functional Test -mA values to be sent using communicator to test a SIF Functio

03/13/2019 12:22 AM

Too many TLA's and MLA's.

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#2

Re: Functional Test -mA values to be sent using communicator to test a SIF Functio

03/13/2019 1:54 AM

..." by injecting a known pressure to the transmitter’s input and measuring the mA output."...

https://blog.beamex.com/2015/12/10/calibrating-a-square-rooting-pressure-transmitter

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#3
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Re: Functional Test -mA values to be sent using communicator to test a SIF Functio

03/13/2019 12:04 PM

..." Operating capacity of the pipeline is 35 MMcfd at the current inlet pressure of 1,200 psi, and 95 MMcfd at 1,440 psi. Current throughput is only 5.2 MMcfd."...

So what is the pressure at 5.2 MMcfd...?

https://www.ogj.com/articles/2000/08/altagas-acquires-two-pipeline-systems-from-transcanada.html

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#4
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Re: Functional Test -mA values to be sent using communicator to test a SIF Functio

03/13/2019 12:41 PM

So we have a 324mm pipeline with a velocity of 20.671m/s and pumping 216,667 cf/hr...what is the pressure?

https://www.engineeringtoolbox.com/natural-gas-pipe-calculator-d_1042.html

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#5

Re: Functional Test -mA Values to be Sent Using Communicator to Test SIF Function

03/13/2019 2:37 PM

If a 4-20mA signal results in a range of 0-40 (MMCFD) for one device and a range of 0-130 (MMCFD) for the other then you just calculate the relationship between the input and output values at the two extremes of the range to find whatever value in the middle you need.

Hint: both transmitters will show a value of 0 (MMCFD) when the output is 4mA and 40 and 130 (MMCFD) respectively when the output is 20mA.

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#6
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Re: Functional Test -mA Values to be Sent Using Communicator to Test SIF Function

03/14/2019 12:15 AM

We’re assuming the summing is done within your control system, so you need to come up with the current for either flow transmitter that adds to your trip level in the control system. Your 4-20mA transmitters have a span of 16mA (20-4), 12mA is half span, 50% of 16mA plus the base 4mA.

You may want to check the circuit operation if the flow output exceeds rated, over 20mA, this can happen, the transmitter is failed, or if the current falls below 3.9 mA, which could be another indication of transmitter or wiring/power supply failure. If you sum a negative number into the calculation, you could prevent proper operation if one of the transmitter outputs dropped below zero. This can depend on your I/O hardware and range configuration, the raw values the module uses to represent the millliamp value appearing at the input. I’ve seen over-range values interpreted as negative for some hardware, really plays hell with your controls if you don’t expect it.

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#7

Re: Functional Test -mA Values to be Sent Using Communicator to Test SIF Function

05/15/2019 10:53 AM

(mA-4)/16 will give you the percent of flow.... unless it is SQRT.

(%*16)+4 will give you the mA output for that.

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