Hart to Current Converter

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The new SMAR HCC301 HART protocol to current converter makes it possible to transfer more information from the field devices into the control room. Useful information such as actual valve position and process temperature that was previously trapped in field instruments are now available for use in sophisticated control algorithms and to improve safety. This can be done without running any additional wires into the field. 

New application capabilities

The HCC301 continuously polls one variable from another HART device and converts it to a dynamically updated 4-20 mA according to a pre-configured range. The polled variable may be the primary variable, primary variable in percentage or one of the dynamic variables: secondary, tertiary and fourth. The HCC301 can also read any device variable available from most devices. The real-time information that now can be extracted from these smart devices can be very valuable. The HCC301 can be used with the DT301 multivariable density transmitter to get a current output for process temperature.


The HCC301 can be used with the FY301 control valve positioner to get an actual valve position feedback current signal for the DCS or PLC. The control strategy can therefore detect a stuck control valve improving safety, provide bumpless transfer all the way down to the valve minimizing process upsets, can be used to detect hunting or sluggish valve performance etc. Most conventional electro-pneumatic valve positioners do not have any actual valve position feedback and traditionally require installation of a second device, a position transmitter, with its own set of levers and wires etc. to provide a feedback to the control room. In fact, a vast majority of control valves have no feedback at all, so operators are unaware if the valve is moving as it is supposed to, is stuck, or is otherwise misbehaving. In fact, most conventional control loops are from this point of view flying blindly waiting for any valve problem to instead manifest itself as an upset process. FY301 with HCC301 makes it possible for the operator at the DCS or PLC to know that the controller output is actually taking effect. Clearly, the safety of the control loop is greatly improved. Some positioners indeed have an optional analog feedback output board. However, this output requires additional wires, effectively doubling the number of wires required. Adding position feedback as an afterthought is very difficult with such positioner. HCC301 is easily added for an FY301 already installed. The HCC301 mounts in the control room panel and requires no running of additional wires into the field and no modification whatsoever to the FY301.



Figure 1: In the past feedback required additional wires (left) but not using HCC301 (right) 

The HCC301 can also be used with the TT301 or LD301 when these are in controller mode, in order to simultaneously also get the process variable to display in a panel meter. The fast 4-20 mA signal goes to the control valve while HCC301 polls the transmitter for the process value and converts it to a reading displayed in a panel meter.


The HCC301 creates new value for existing products. Making full use of HART can breathe new life into a system extending its useful life by a few more years. 

Easy to install

The HCC301 is DIN-rail mounted and therefore simply snaps into the control panel. The HCC301 is a loop-powered two-wire device just like a HART transmitter and is therefore very easy to wire. The HCC301 is completely self-contained and extremely compact, and runs from a regular 24 VDC supply.

This makes it very easy to replace old electro pneumatic valve positioners connected using only a single pair of wires while adding position feedback at the same time at little additional cost. Running new wires for a 4-20 mA feedback from the valve back to the controller is time consuming, costly and requires additional permissions. A more attractive alternative is to use a FY301 that feedbacks the actual valve position using HART communication. Even though the control system does not support HART this is not a problem because in the control room a HCC301 is installed. The HCC301 produces a 4-20 mA signal that connects to any existing control system. I.e. therefore there is no need to replace the control system hardware to enjoy this HART functionality.

Similarly, the HCC301 converter can be used with multivariable transmitters to let legacy systems gain access to auxiliary variables such as the process temperature from DT301. The DT301 density transmitter also measures process temperature which using the HCC301 becomes available as a 4-20 mA signal that connects to the control system. This way operators and the control strategy can also monitor the temperature of the product in the tank. 

Easy to configure

The HCC301 is extremely easy to set up, even by non-experts. Configuration is done by means of the user friendly HPC301 hand-held. The hand-held is also used to calibrate the current output of the HCC301 if required and can retrieve other useful information pertinent to the converter.



The communication diagnostics in the HCC301 detects communication failure on the HART network and sets the output to a pre-configured safety value of 3.6 or 21 mA as per the NAMUR NE 43 standard to indicate failure allowing the receiving controller to take safe action. The user configures the maximum number of communication retries permitted before the failsafe is activated. 


Because the HCC301 operates as a primary master and the HPC301 and other hand-helds as a secondary master, both can be connected at the same time. Because of the interoperability of the HART protocol, HCC301 is compatible with all HART devices. Therefore, the data can be accessed from any HART device from any manufacturer. The polling of the field device is very fast ensuring that the current is updated quickly.

Accuracy of the variable converted will be 0.040 % of the span.
Temperature Effect
0.2 % in the output current from -40ºC to +85ºC.
Power Supply
12 to 45 Vdc in the 4 to 20 mA. This voltage will supply the HCC301.
Via HART, passive MAU and isolation of 1500 Vdc.
Response Time
Updating of the read variable within 120 ms.

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