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which is better: 2-wire or 3-wire transmitter

Dear Sirs,

 

 

I am going to buy two NI modules 9203. The problem I am facing now is related to the transmitters (pressure transmitter and resistance thermometer). The output of the transmitters is 4-20 mA. I have the option either to get the transmitter with 2-wire or 3-wire output. 

 

I want to know which is better regarding the accuracy of the readings and the noise, taking into account that the cable will 5 meter long.

 

 

Thanks for your help.

 

 

 

Yours,

Ehab

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Hi Ehab,

 

What are the manufacturer and models of the sensors that you are looking at?

Regards,
Jim Schwartz
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Dear Sir,

 

 

Here are the details:

 

- Pressure transmitter P-30: 4-20 mA, 2-wire or 3-wire:

 

http://en-co.wika.de/upload/DS_PE8154_GB_13168.pdf

 

 

- Resistance Thermometer TR30-W: 4-20 mA, 2-wire only

 

http://en-co.wika.de/upload/DS_TE6030_GB_12664.pdf

 

 

 

 

Waiting for your reply .........

 

 

 

 

Yours,

Ehab

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Hi Ehab,

 

Both of them should be fine, but from the spec sheet of your pressure transmitter, it looks like you can sample a little faster with the 3-wire.

Regards,
Jim Schwartz
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Dear Sir,

 

 

Thank you for your reply.

 

First, how do you know that the 3-wire can sample faster, the response time is the same (1 ms).

 

We will have 8 Sensors (pressure + temperature) and it will be connected to the same DC power supply. This means that the positive lead of all the sensors will be connected together as the positive lead of each sensor will be connected to the same power supply. Do we have any problem here ? Is there any specifications for the DC power supply ?
 

 

Yours,

Ehab

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From the spec sheet, it says that the measuring rate is 1 ms with the 3 wire and 3 ms with the 2 wire:

 

 

response time.JPG

Regards,
Jim Schwartz
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Dear Sir,

 

 

Thank you for your reply.

 

We will have 8 Sensors (pressure + temperature) and it will be connected to the same DC power supply. This means that the positive lead of all the sensors will be connected together as the positive lead of each sensor will be connected to the same power supply. Do we have any problem here ? Is there any specifications for the DC power supply ?
 

 

Yours,

Ehab

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Message 7 of 10
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BUENAS NOCHES

 

ESTOY UTILIZANDO LA NI USB 9219, PERO TENGO NO SE COMO CONECTAR  EL SENSOR H2S QUE ES DE 2 HILOS A ALIMENTACION Y A ESTA TARJETA. ANEXO SIN EMBARGO LAS ESPECIFICACIONES DEL SENSOR.

 

 

GRACIAS

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Message 8 of 10
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In industrial nomemclature, a two wire transmitter is powered by the receiving device over the same two wires as the signal (4-20mAdc). The power is typically 24 VDC.

A 3-wire transmitter requires two wires for signal and three additional wires for power.

There are howevr some dc powered transmitters with special shielding that use a three wire connection. It must be compatible with both the transmitter and the reciever.

 

Another tip is to always use a 4 wire RTD for maximum accuracy up to hundreds of meters. For short runs a 3-wire RTD will usually be satisfactory IF all three wires are of equal rresistance.

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Message 9 of 10
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good topic,I also want to know the result.

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