Stability and safety considerations of the 2-wire transmitter

- Mar 08, 2019-

The industrial environment is harsh and requires high reliability. Therefore, the design of the two-wire transmitter needs to consider certain protection and stability measures.

1.  Power Protection

Power supply reversal, overvoltage, and surge are common power problems in the industry. The reverse connection of the power supply is the most common error when the device is installed and wired. A diode can be connected to the input port to prevent damage to the circuit when the power supply is connected. If a full-bridge rectifier is added to the input, it will work even if the power supply is reversed.

In order to prevent lightning, electrostatic discharge, surge and other energy damage to the transmitter, a TVS tube can be installed at the entrance of the transmitter to absorb the instantaneous overvoltage energy. Generally, the TVS voltage value is slightly lower than the operational amplifier limit voltage to protect. If it is possible to be struck by lightning, the TVS may not absorb enough capacity, and a varistor is also necessary, but the leakage of the varistor itself may cause some error.

 2.  Overcurrent Protection

There may be errors such as sensor disconnection or short circuit during the operation of the device. Or the input quantity itself is likely to exceed the range. The transmitter must ensure that the output will not rise without limit under any circumstances, otherwise the transmitter itself, the power supply, or the remote display instrument may be damaged.

3.  Wide Voltage Adaptability

Generally, two-wire transmitters can adapt to a wide range of voltage changes without affecting accuracy. This allows for a wide range of power supplies and accommodates large load resistors. The most sensitive part of the power supply is the reference source, and the reference source is also the main component that determines accuracy.

 4.  Untwisting Capacitor

In general circuit design, there is an untwisting capacitor at the power supply end of each integrated circuit. When a two-wire transmitter is powered up, the charging of these capacitors can cause large currents in an instant, potentially damaging the remote meter.