Hi fellows;

I have three Differential transmitter range 0 to 200 inches of water col. Please guide me on which port means high side or low side i apply the pressure?

either if any have literature about the connection technique of differential transmitters plz send me a link. About in what condition i connect the high side or low side to the measuring setup.

Thanks
Ashraf

 

Hi there,

By looking at the question you have asked, I think giving you the answer is not going to help you much at all. Let me explain. It is like driving a car. The level of your question is the same as when you ask someone how to get into the car. The answer is of coarse that you need to open the door first before you can get into the car but this is not going to help you much since you still cannot drive the car.

Let us know exactly what you need to do and what type and size transmitters you have to work with and we will send you a complete procedure on how to do the installation and calibration. Give as much detail about your application as you can, and tell us where you need to send these signals to, and so on. The more details you can provide the easier it will be for us to give you advice and help.

 

Hi there;

Ok. The differential transmitter is zero to 200 inches of water col from rosemount model 3051.

It is connected to measure the Venturi differential pressure. Now can u tell me how i calibrate it?

Secondly it is connected to the analog module and then data transfer to the PLC 1756-51. From Rockwell.

Now i want to know the principle of operation of the differential transmitter. If i apply the pressure on the L side while H side is open to atmosphere the reading is in negative if i apply the pressure to the H side while L is open to atmosphere the reading is positive. In the system the reading of the venturi differential is positive. Can i say that the transmitter is used as +ve displacement technique?

Thanks

 

Hi again,

If I look at your question it seems like you are set and determined to measure the differential pressure only across the venturie but I think I should make you aware of the fact that the differential pressure across the venturie is not going to give you a direct flow measurement, if that is really flow you want to measure. I suspect it is if I look at the kind of restricting element you use.

I also know the ranges available on the 3051 transmitters and the 200 inches is not one of the ranges available. If I convert it to mBar it comes to 500mBar which seems more like a calibrated span value for a typical flow application.

Sorry but I cannot keep on guessing what you want to do. Good luck!!!

 

principle of operation of the differential transmitter:

Internally, the low side applied pressure is subtracted from high side applied pressure. That difference value is the DP.

The 4-20mA output scaling depends on how the transmitter is setup: linear pressure or square root, and its range.

If i apply the pressure on the L side while H side is open to atmosphere the reading is in negative if i apply the pressure to the H side while L is open to atmosphere the reading is positive.

That's what is supposed to happen. The high side connects to the inlet end of the venturi, the low side to the outlet end of the venturi.

>In the system the reading of the venturi differential is positive. Can i say that the transmitter is used as +ve displacement technique?

I don't know. I'm not familiar with your terminology.

The transmitter can transmit either the raw differential pressure, or do it can calculate the square root and output a derived flow value. The square root operation should be done only once, either in the transmitter or at the receiver device, not in both places.

The manufacturer's sizing sheet data for the venturi specifies what DP value corresponds to a max flow rate for that model/size venturi. That is critical information in order to match a DP to flow rate for that venturi.

 

Hi Sir;

Thanks for explanation. A lot points are cleared. Can u also help me about the SQRT function of the DP transmitter?

For example the data is from DP transmitter is raw and calculate flow in the acquisition system. Just for display but the flow is calculated in the acquisition system. How can i know the transmitter function is raw or sqrt, already configure by the manufacture or supplier?

can i know about the seeting of sqrt by hart communicator? I have Fluke 744 calibrator.

Thanks for help
Bye

 

> How can i know the transmitter function is raw or sqrt,already configure by the manufacture or supplier? <

One way is to apply a low pressure, and note the 4-20mA output value (example: output = 5.5mA)

Double the pressure. Did the output double?

(Example: 7.0mA is doubled value
5.5 - 4.0 = 1.5mA
7.0 - 4.0 = 3.0mA
3.0 is 2x 1.5mA
(accounts for the fact that zero pressure is 4mA, not 0mA)

If the output value doubled, then the transmitter is linear and represents the differential pressure.

If the output value did not double, then the transmitter is in Square root mode

> can i know about the seeting of sqrt by hart communicator? I have Fluke 744 calibrator. <

I believe linear square root is one of the basic HART functions, so you should be able to read the basic parameters with the Fluke, even if you don't have the DD or DOF or whatever Fluke calls the device descriptor file for that brand/model.

For details, see the instruction manual.

If the transmitter is not installed in a loop, you'll need ~250 ohms in the loop to read the HART data. I'm sure Fluke has some means of doing that.