Analog Test Filter
The Analog Test Filter is a specially designed low pass filter used for testing device implementations to confirm that the HART digital signal will not interfere with the 4-20mA analog signal. The filter is also used for testing Carrier Start/Stop transients. A Butterworth type lowpass filter has a pass band of 0 - 25 Hz and 2nd order roll-off above 25 Hz. The test filter has a gain of 10X which the test data sheets take into account in the test criteria.
Digital Test Filter
The Digital Test Filter is a specially designed band-pass filter for testing device implementations to confirm that changes in the 4-20mA analog signal will not interfere with the HART communication signal. The Filter is also used to confirm that noise generated by the device will not interfere with HART communication. This filter is necessary for the Output Noise During Silence and Analog Rate of Change tests. A Butterworth type bandpass filter has a pass band of 500 Hz to 10 kHz, 2nd order rolloff below 500 Hz, and 1st order roll-off above 10 kHz. The test filter has a gain of 10X which the test data sheets take into account in the test.
FSK Physical Layer Test Interface
The PhL Test Interface is the required PC interface for Physical Layer testing. The output amplitude of the PhL Test Interface is adjustable. It provides a suitable PC interface for all Physical Layer testing, however, the proper transmit amplitude must be verified before conducting each test. The PhL Test Interface is a custom modified HART modem with RS-232 interface.
The tool has a no-stop pot for adjustment of the output signal amplitude. Since the pot is no stop, turning it either direction any number of turns will not effect the pot performance.
The maximum reduction in signal is achieved by turning the pot 5 turns counterclockwise. If you are using a desktop PC and a 250 Ohm load, the typical minimum output will be 60mV. You can put a scope across the 250 Ohm resistor to see what is coming out of the modem.
Desktop PC serial ports typically output 4-6V. Many notebook PC serial ports output much lower voltage. The MODEM is designed to work at 4V, but can work down to 2V though it is not guaranteed.
The maximum signal amplitude adjustment occurs when the pot is turned 5 turns clockwise. The maximum signal from the modem across a 250 Ohm resistor will be 1.6V.
Software Support for Physical Layer Test Interface
Xmtr-MV is an MS-Windows based application that simulates a HART device. Its main purpose is to support engineers developing and testing a HART master. It is a HART 5, 6, and 7 compliant. This tool is currently being used to support the QA program, SDC, HART Server, 375 and the writing/maintaining of the "new DDL structure" Standard DDs (HART 5, 6, and 7).
ModFiles - Xmtr MV supports the *.mod files. The intent of these files is to make Xmtr-MV act as misbehaving slave. Although, the power of these files can be used to change the behavior of Xmtr-MV for any purpose.
Special Hardware Instructions:
Communication – XMTR-MV can communicate with a host application via either a "cross over cable or NULL modem cable" or connection of two HART modems (one for master and one for XMTR-MV).
PortMon - This application can be easily installed on a PC to monitor any serial port's communication. It is excellent tool to capture log files of the HART communication for troubleshooting purposes. This tool has been sent to customers to help examine their QA issues.
Software used when the Device Under Test (DUT) is a Slave. The software is capable of emulating certain specific functions of a HART master.