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HART Pass Through IO Cards
HART Pass Through IO Cards

The IO cards to be Hart Pass Through. what is the Meaning of this? Kindly describe? Is that means AMS system to be required?

What type of alters are generally available through HART pass through cards?

One might assume that any HART enabled analog input card would be able to deal with the primary variable from a field transmitter, just like a non-HART enabled AI card gets the process variable via a 4-20mA signal. The AI card's connection to the HART field device makes the AI card the portal for the HART process variable(s) and, typically, the data associated with the universal and command HART commands.

But how does the AI card deal with data other than the variables and universal and common HART data?

HART commands relating to configuration, required for setup, calibration and commissioning (frequently integrated into asset management programs), or commands asking for diagnostic data need to get out to the field device and the return data from the transmitter need to be directed to the host application.

A 4-20mA loop isolator's ability to pass HART data through from one side to the other is often called HART transparency, an important feature when using HART because many isolators strip the HART signal off and pass only the analog 4-20mA through the isolator.

In a fashion analogous to transparency, HART commands and the response data "pass through' the AI card to a host application. The commands are generated by a host application, 'pass through' the AI card to the field device and when the return data arrives it is ported (passed) through the AI card to the host application.

By Jonas Berge on 23 November, 2013 - 8:00 am

"HART pass-through" means the control system I/O card supports the HART protocol, passing HART commands through from Intelligent Device Management (IDM) software part of the Asset Management System (AMS) to HART devices in the field.

See clause 5.6 in the "Device Diagnostics Deployment and Adoption Guide" found here:


By gbmewada on 7 June, 2018 - 5:49 am

HART Pass Through device can be elaborated as follows.
Generally devices are connected as follows:
Transmitter output given to --> Signal Isolator output given to --> PLC/DCS.

Now, Some Transmitters are programmable by HART protocol. Where as, Signal Isolators are suppose to block signals above 100Hz, to eliminate noises basically. Since Isolators are connected between Transmitters and PLC/DCS system, person thriving to program Transmitter using HART from PLC/DCS side will not be able to do so, because Isolator will eat all HART signal due to its bandwidth limitation and unidirectional property.

Hence, one has to design Isolator that can allow HART signals to Pass through it from both the sides i.e. Input to Output and Output to Input...