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4-20mA Analog Output Transmitter with HART Modem or without HART Modem



The HART1X, HART2X are 4-20mA anolog output modular transmitters, optionally embedded with the DS8500 HART Modems from Maxim Integrated.

These modules convert an USART input message frame into an analog voltage, by using PWM with at least 12-bit resolution. The volrate is then converted to analog current and outputted to the AO terminal.

The HART1X requires a 24VDC power supply under both loop-powered mode and self-powered mode. In loop-powered mode, the positive loop input, LOOP+, should be connected to  LPIN and the negative input, LOOP-, should be connected to the AO terminal.

The HART2X, on the other hand, is powered by loop current; therefore no power supply is required to operate. Loop+ and LOOP- should be connected to LPIN and AO respectively.

Another major difference between those two modeuls is that the HART1X can product analog current from 0-20mA. The 0-4mA current can be used to indicate negative values in some applications.

The 4-20mA can be used for MCU-based measurement of the following product;

1) Flow

2) Level

3) Temperature

4) Pressure

Technical features:

1)USART Driven, one photo-coupler required for standard operation

2)HART1X for self-powered operation; HART2X for loop-powered operation

3)Comply to HART physical layer requirements

4)12-bit resolution

5) Small size: 8.8×27.5×17.1mm

6)Low cost

Absolute Maximum Ratings

Voltage range on AO,+24,LPIN, relative to GND                                     -0.5V to +40V

Voltage range on  pins, except AO,+24,LPIN, relative to GND              -0.5V to +3.6V

Operating temperature range                                                                      -40 to +85 Degree C.