4-20 milliampere transmitter

Details 4-20 milliampere transmitter 4-20 milliampere transmitter

1986-08-28

1988-07-19

Caldwell, Sr., John W.

Communications: electrical

Continuously variable indicating

Condition responsive

340507, 340652, 34087039, G08B 2100, G08C 1902

Patent

active

047588373

ABSTRACT:
A transmitter circuit adapted to be connected to a sensor and generate a 4-20 milliampere signal proportional to the output of the sensor includes a first amplifier which is connected to the sensor and has an output voltage proportional to the sensor output voltage. A predetermined reference voltage is supplied to a reference input of the first amplifier. A second amplifier housing an output voltage responsive to a difference between its input voltages, has its output connected to the gate of an output transistor, preferably a fluid offset transistor. An output resistor is connected between the positive power supply and the source of the output transistor. The output of the first amplifier is supplied to the positive input of the second amplifier and the voltage at the source of the output transistor is supplied to the negative input of the second amplifier. The output current for the transmitter is generated at the drain of the output transistor. If any of the positive power supply wire, the current output wire or the common potential wire should break, the output current of this transmitter circuit drops to zero.

REFERENCES:
patent: 3492589 (1970-01-01), Rotier
patent: 4194195 (1980-03-01), Merrell et al.
Tony Wang, Burr-Brown Corp. Current Transmitter IC Cates to High-Level Signals and Tight Budgets, Electronic Design, Apr. 18, 1985, pp. 165-174.
Burr-Brown Corporation; Precision Voltage-To-Current Converter/Transmitter; Nov. 1984, pp. 1-8.
Paul Brokaw, Analog Devices Inc., Versatile Transmitter Chip Links Strain Gauges and RT Ds to Current Loop; Electronic Design, Apr. 18, 1985, pp. 153-163.

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