Abstract: An AC to DC converter circuit 300 includes a transformer 316 having primary 314 and secondary 320 windings, a rectifier bridge 322 coupled to the secondary winding, a DC filter capacitor 328 coupled to the rectifier bridge, a voltage regulator 330 coupled the DC filter capacitor and to DC output contacts 332, 334. The converter circuit includes an AC reactance 312 coupled in a series circuit with the primary winding and AC input contacts 304, 306. The AC reactance limits AC excitation voltage at the primary winding to less than the AC line voltage.

Abstract: A method for preventing unsafe transmission on an incompatible network with a multi-protocol intrinsically safe handheld field maintenance tool as provided. The method preferably includes checking voltage levels on two sets of network connections when a network connection is detected or indicated on one set. If incompatible voltage levels are detected, the field technician is warned. If voltage levels are appropriate on a selected set of network terminals, the method continues by listening for network traffic of the selected network type. In this manner, a multi-protocol intrinsically safe handheld field maintenance tool is operable with multiple process control communication protocols while minimizing the risk of incompatible data/signal transmission upon process communication loops.

Abstract: A method for preventing unsafe transmission on an incompatible network with a multi-protocol intrinsically safe handheld field maintenance tool as provided. The method preferably includes checking voltage levels on two sets of network connections when a network connection is detected or indicated on one set. If incompatible voltage levels are detected, the field technician is warned. If voltage levels are appropriate on a selected set of network terminals, the method continues by listening for network traffic of the selected network type. In this manner, a multi-protocol intrinsically safe handheld field maintenance tool is operable with multiple process control communication protocols while minimizing the risk of incompatible data/signal transmission upon process communication loops.

Abstract: A hand-held communication and diagnostic tool is provided. The tool is able to automatically detect connection to a process control loop as well as detect the type of loop to which it is connected without substantially disturbing messaging on the loop. Once the tool determines the type of loop to which it is connected, it provides suitable communication and diagnostics appropriate to that specific type.

Abstract: A hand-held communication and diagnostic tool is provided. The tool is able to automatically detect connection to a process control loop as well as detect the type of loop to which it is connected without substantially disturbing messaging on the loop. Once the tool determines the type of loop to which it is connected, it provides suitable communication and diagnostics appropriate to that specific type.

Abstract: A low power transmitter has a D.C. Power supply for providing the transmitter with power. The supply is coupled to a voltage regulator for regulating the voltage to the transmitter and the regulator is further coupled to an oscillator which provides a time varying voltage signal to a capacitance sensor which varies as a function of the parameter to be sensed. The charging and discharging current pulses from the sensor, as affected by such sensors, are rectified and fed to an oscillator driver amplifier which controls the time varying voltage as a function of such rectified signals. The rectified signals are also fed to a low power consumption output amplifier which provides a zero based D.C. voltage output signal representative of the parameter to be sensed along two wires. The transmitter operates on low voltage and has a low power consumption.

Abstract: A current isolation circuit converts a pulse width modulated input signal to an isolated DC output current whose magnitude is a function of the duty cycle of the input signal. The isolation circuit includes an optical isolator which receives the pulse width modulated input signal and has an output which changes between a conductive and a non-conductive state in response to the input signal. A voltage regulating diode, such as a Zener diode, is connected to the output of the optical isolator and to an isolated power supply so that the voltage across the Zener diode varies between two known voltage values in response to the switching of the optical isolator output between conductive and non-conductive states. A signal derived from the Zener diode is filtered to produce a reference signal with a magnitude which is a function of the duty cycle of the input signal.