Micron Instruments' Miniature 4-20mA Pressure and Temperature Transmitters

Herbert Chelner, CEO and Chief Scientist
Dr. Robert A. Mueller, President and General Manager

Micron Instruments offers a product family of 4.0 to 20.0 mA pressure and temperature transmitters: models MP402, MP502, MPT402, and MPT502

Most suppliers typically refer to these 4-20 sensors as “current transmitters”. In fact, these sensors sink a fixed current, even when the power supply or line resistance between the sensor and the power supply varies. There are several important benefits of this property.

If measurements need to be made over a long distance, such as in a large ship or airplane, or down water or gas wells, and the temperature varies, the line resistance will vary as well, causing the sensor to be inaccurate.

The MP402 and MPT402 also have a flush diaphragm for flush mount applications such as water tunnels or oil lines or where higher frequency response is required

The MP502 and MPT502 have male threads for ease of application

The electronics in Micron’s transmitters sink 4.0 milliamps at zero pressure. The user may select, within the operating limits of the system, the amount of voltage change due to pressure or temperature by putting a resistor in series with the power supply, usually in close proximity to the power supply. If the user decides to use 250 ohms, the voltage drop across the resistors would be 1.0V at zero pressure. Four (4.0) mA times 250 ohms is one volt. At full scale, the electronics sink 20 mA times 250 ohms, which is 5.0 drop across the 250-ohm resistor. Zero to full-scale pressure is 1V to 5V, and should be linear and proportional to the pressure being monitored. Altering the voltage change due to pressure or temperature can be achieved by increasing or decreasing the line resistor, provided it does not exceed the power (voltage) available.

Only two wires or one wire and a ground are required to obtain the signal, allowing the electronics to compensate for voltage and line resistance changes, and also minimizing cable cost by reducing the number of wires required.

Micron’s 4-20 transmitters offer a great solution for remote measurement of water level in wells or around dams. Such monitoring systems can utilize wireless communication transceivers powered by rechargeable photoelectric batteries at the top of the well, to provide real-time data acquisition and system management. Even in cases where the battery voltage varies with temperature but remains within operational levels, the sensor will compensate and report accurate liquid levels. In case the battery voltage drops below the operational level, the system and could report a “temporarily inoperative” state.

Micron’s 4-20 transmitters sensors are made of Titanium 6AL4V, which is corrosion resistant and can remain in water (and even contaminated water) for long duration's without degradation of performance. These sensors have a double-molded outside jacket designed for continuous use in water for extended periods.

Want to Learn More? Interested in Collaborating?

Whether you’re interested in pursuing this type of design, or another measurement related application or design, please contact us for a free, confidential consultation either by email using our Contact Us Form or phone (805-522-4676).

European companies can directly contact Haptica SrL, Micron’s exclusive European re-seller, through info@hapticasensing.com. The Haptica Team is fluent in German, Italian, English, and French. They offer technical consultation in cooperation with Micron’s technical leadership.