XMTR-MV is a useful tool for testing communication with a host. The XMTR-MV software runs on a PC and communicates using a HART registered Modem (for example a USB HART modem). The modem is a medium impedance device per the physical layer specification and does not offer a current loop. Most controllers, PLCs, and other HART masters will expect a loop current.
To use the XMTR-MV on a PC connected via a small circuit to simulate a loop current. It is best to target a 12mA current loop. See "Connection of XMTR-MV to PC running Master Application" for an example.
To use the XMTR-MV on a PC connected in parallel with an actual device, see "Connection of XMTR-MV to I/O System".
Connection of XMTR-MV to PC running Master Application
The 1750 Ohm resistor can be replaced by a 2-wire transmitter at a polling address greater than XMTR-MV. By default XMTR-MV starts at polling address 0. A transmitter with non-zero polling address could replace the 1750 Ohm resistor.
The purpose of the 1750 Ohm resistor is to prevent the loop current from exceeding the power capacity of the 250 ohm resistor. A high wattage resistor may be used for the 250Ohm resistor to eliminate the 1750 Ohm resistor.
Connection of XMTR-MV to I/O System
Many I/O systems include detection of open circuit and short circuit; therefore the XMTR-MV device simulator must be placed in parallel with an actual transmitter. The connection is made by placing a transmitter at a non-zero address for proper impedance then connecting the XMTR-MV.
The 2-wire transmitter could be replaced by a circuit to simulate a HART device. This could be a simple RC circuit to trigger the I/O channel. Specific system vendor documentation may include recommended simulation circuits for loop test.