4
HART Compliance
SVI requires a HART-compliant communications loop. The HART protocol specifies the noise level,
impedance requirements and configuration of the loop.
Conventional current output loops consisting of the following components usually meet requirements for
HART compliance.
•
Quality current source (e.g. low noise, high impedance)
•
Minimum loop impedance of 250 ohms
•
Twisted pair cable suitable for 4-20 mA current loops
Failure to Communicate
If the PC fails to communicate with the SVI (the PC displays the message “No Hart Device” or “Device
Not Responding”) then the PC cannot establish a link to the SVI. Possible causes of communications
failure related to installation include:
•
Poor wiring contacts
•
Improper connection of the HART modem to the computer
•
Incorrect serial port
•
Using ValVue with another HART master terminal in service
•
Insufficient loop impedance (Require a minimum of 250 ohms)
Note:
When an intrinsically safe barrier separates the communicating device, a HART-
compliant barrier must be used.
Note:
If there are suspected HART compliance problems, prepare a detailed description of the
loop, including all devices on the loop, type of wiring used, loop length, and presence of
any possible interference sources before contacting the factory for assistance
Note:
You cannot use ValVue and attempt to connect another HART master terminal device
(e.g., a hand-held device). ValVue will not operate with a second terminal device (either
primary master or secondary master).
