Hi- A customer was asking about analog output scaling for Ebtron transmitters— Here is a good place to start:
Probe based airflow stations come default as 0-5000 feet per minute (FPM) on the analog output 1 from the transmitter . Note that this is a VELOCITY and not a VOLUME.
Fan inlet airflow stations come default as 0-10,000 FPM since they are generally a faster speed into the inlet cone.
For most systems, we recommend that you bring all of the transmitters velocity analog output (either 0-10v or 4-20ma based on the dipswitch) into your control system Analog Input (AI) as the same analog scaling— that is, regardless of duct size all of your Ebtron probe transmitters will have the same 0-5000FPM scaling into your AI. We like bringing all of the transmitters in with the same scaling to avoid field confusion— at least initially.
Take each AI and multiply it by the duct area to get an AV showing the VOLUME in CFM.
VELOCITY x DUCT AREA = VOLUME FLOW
Having the volume flow be an AV allows you to do other operations on it later that you cant do with an AI*. We can lookup the area from the packing slip if you don’t have it— call us if you need this value.
*Useful AV operations: You can write a “0” to the AV on a windy rooftop when the unit is off, so there aren’t any weird airflows on the screen to distract the operators.
Here is a math example-
If you brought the 0-10v signal in as 0-5000FPM on a 4’x4’ duct:
5000FPM x 16Ft^2 = 80,000CFM at max flow. This means that 5V at the transmitter should show 40,000CFM on your EMCS display.
Here is how the manual describes it, we did the “manual conversion”:
USING THE TESTOUT BUILT INTO THE TRANSMITTER:
Ebtron gave us a great tool to help commission this- by going into the setup/tools menu you can force the output to a certain %, and verify that we did all of the steps correctly. If I command the output to 50% I can measure 5v on the output and should see the EMCS display change to 40,000CFM in the above example.
As always, please call us if you have any questions.