Hart Modems.

HoldenC

Member
Join Date
Sep 2012
Location
Cumberland, KY
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215
I recently picked up a Viator Rs-232 Hart Modem to be able to calibrate a couple devices we recently acquired.

I have a couple questions if anyone can help.

1.) I have a question about adding the 250 Ohm resistor. I keep seeing information about adding the resistor in a test bench situation. Would I still need to add it if the unit is currently in use ?

2.) Is there a generic program I can run that can mimic a Hart Communicator ? I have some specific programs I have for the devices we have, but I wanted to use it on other devices as well.

Thanks in advance.
 
When connecting to a HART device I usually try to connect without the additional resistor and only add it in if needed. If the device is already installed and you are connecting in the panel, there is usually enough resistance in the line.

I recently connected 6 flowmeters to one of these and used PACTware to configure. Not sure if it is compatible with the device you got but it might be worth taking a look .


https://www.phoenixcontact.com/onli...=usen&pcck=P-13-21&tab=1&selectedCategory=ALL
 
1. Sometimes you do have to add the 250 ohm resistor to existing loops.

Lots of existing loops already have 250 ohms or input resistance on the analog input. But that's by no means a given. Some input resistances are 10 ohms, some 50 ohms, some 100 ohms, it's all over the map. Rarely are analog inputs more than 250 ohms.

A 24Vdc power supply will drive 20mA thought 500-600 ohms of loop resistance. You can usually add the 250 ohms in the loop since the copper wire is usually negligible (depends on the distance and wire gauge), and an analog input resistance of 250 and 250 for your HART resistor will not load the loop to where the power supply can't drive the full 20mA.

On the bench, with a 2 wire transmitter with just a power supply, the power supply will 'eat' all the HART signal and you'll never get a HART connection with the resistor.

2. Pactware is freeware software but it has a significant learning curve. Try Vega's or Krohne's version which are still "open".

Pactware requires
- a HART driver which is free that enables HART communications.

- the vendor supplied DTM file for the specific device. Not all HART devices have a DTM.

I've heard that there's a generic HART driver for 10 basic HART commands, but I believe it's licensed driver, not a freeware driver. For use with Siemens devices there's a driver that enables the DTMs (I don't think any other vendor requires a DTM driver).

3. Be warned that the old Mactek serial modems can be flakey when run on USB/RS-232 ports.

Notes from serial port days - port setting change for the Mactek:

For serial HART modems, in Win XP Pro;
change the COM port buffer setting to ‘low’
- Right-click on 'My Computer'
- select Properties >Hardware > Device Manager > Ports > (expand) > Communications Port (COM 1…8)
- double-click COM connection (i.e. COM1)
- Properties > Port settings > Advanced...
- Either uncheck “Use FIFO buffers . . “ or set the value for both the transmit & receive buffers to ‘low (1)’
- Restart Windows for changes to take effect

4.For Mactek USB HART modems, Windows 10 requires the latest version Mactek'.s

SN 314386 and prior only work on Windows 7 and prior
SN 314387 and after work on Windows 10
 
Im actually needing to program a Vega VegaPuls67 and a Ohmart-Vega Gen-2000 density meter.

The VegaPuls67 uses PACTware, and the density meter uses "Ohmview". Im still trying to find some more information before I attempt this calibration in a running environment.
 
Thanks for the help. I have recently downloaded the Vega DTM collection.

Our facility that has these devices is about 3 hours away. So, it may be a while before I can make my way back over there.

However, we do have several Rosemount 3051 level transmitters that allow for Hart Communication as well. I may see what it takes to be able to connect to one of them.
 
My opinion: Pactware is sufficiently non-intuitive to warrant experimenting with it before you show up on-site. I'd suggest connecting to any HART device to get an idea of how the software works.
 
This morning I am able to be at a site this is down for the weekend. I am trying to connect to a device, but Im not making it anywhere.

I have installed Pactware from Vega.
I have installed Vega and Emerson DTM's.

I found a Project Assistant that tried to search for devices, but I get a message about the search being ended.

Can anyone point me in the direction of some information to help a newbie get started. Im trying to connect to a Emerson Rosemount 3051.
 
Do you have a real serial port on your computer? I've had mixed results with using a USB to serial converter with my old serial HART modem.
 
Mactek had a utility program, the Viator Check Utility, that would poll the device for its primary variable once per second. When that worked, you knew that HART communications could be established via the COM port and modem to the field device.


The program might have been included with the general software package, but Mactek might still post it on its web site.
 

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