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The resistor doesn't have to be 250 Ohms, anything from 100-600 will work equally well. The power supply is a low impedance to the hart signal shorting it out. Adding the resistor raises the impedance so that the signal can be detected by the calibrator. A small reactor would also work.

Ohms law states that a resistor must be present with current to receive a voltage (V=IR) this resistor converts current to voltage which is used as a digital voltage signal. (1-5 V).

The HART protocol uses 1200 baud Frequency Shift Keying (FSK) based on the Bell 202 standard to superimpose digital information on the conventional four to 2OmA analogue signal.

Hope this may help ful....

Sudhan.S

shansudhan@rediffmail.com

Q: Why you need 250 ohm resistor in hart?

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You need to calculate the equivalent resistance. For instance, if the three resistors are connected in series, simply add all the resistance values up. Then, you calculate the current (in amperes) using Ohm's Law (V=IR); that is, you need to divide the voltage by the resistance.

I don't see a question. Please clarify if you want an answer.

Rt = 10

No such resistor exists. Any resistor placed in parallel with a 6.0 ohm resistor is going to reduce the combined resistance below 6.0 ohms.

The combined resistance will be 2 Ohms.

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You need to use the 250 Ohm resistor in series with HART protocol communication because it acts as a shunt resistor.

In this situation, to calibrate a transmitter you need a power circuit and communicator circuit. The Hart communicator used in the calibration process is connected to the power source circuit in parallel. The power source circuit is the one that has ammeter, 250 Ohm resistor, and power source all connected in series. As the transmitter sends output mA, it creates volt drop across the 250 Ohm resister. Let's say the volt drop across the resistor was 1 Volt. Now, back to the Hart communicator. It is a load, meaning there will be a volt drop across the Hart communicator. Since it is in parallel with the power circuit, it is also parallel with the resistor. So, the 1 volt drop across the 250 Ohm resistor will also make 1 volt drop across the Hart communicator. Technically speaking, the 1 volt drop across the Hart communicator is only true if its resistor is also 250 Ohm. However, it does NOT matter what voltage drop is in the Hart communcator. It only sees the "relative" voltage drop changes to measure the changes in transmitter outputs.

Why would you buy something that does absolutely nothing? If you need a "zero ohm resistor", just don't connect any resistor at all.Why would you buy something that does absolutely nothing? If you need a "zero ohm resistor", just don't connect any resistor at all.Why would you buy something that does absolutely nothing? If you need a "zero ohm resistor", just don't connect any resistor at all.Why would you buy something that does absolutely nothing? If you need a "zero ohm resistor", just don't connect any resistor at all.

Green Red Brown

The current would be about 20 volts.

1amp

No. 2.2K ohm is 2200 Ohms.

3

You need to calculate the equivalent resistance. For instance, if the three resistors are connected in series, simply add all the resistance values up. Then, you calculate the current (in amperes) using Ohm's Law (V=IR); that is, you need to divide the voltage by the resistance.

You need to provide values of resistor and inductor etc to find the phase angle.

I don't see a question. Please clarify if you want an answer.

2