| Q |
When using AMS software the MTL4841 is recognised but the attached devices are not found?
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| A |
This usually means that the MTL4841 is in the wrong mode. The MTL4841 is available in three different pre-set modes, MTL, AMS and PRM and should be ordered in the required mode to suit your Instrument Manager Software (IMS). If you are unsure which mode your IMS requires, please contact your local MTL representative. |
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| Q |
After resetting the IMS, not all devices were found. Performing another reset resulted in a different list of devices found. What is happening?
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| A |
This is often because the converter is either not a recommended type or the settings are not correct. MTL recommends using the Westermo MA-45 RS485 converter with the MTL4841.
Lack of termination and biasing can be another reason for seeing this effect. The RS485 serial line should be terminated and biased and the Westermo converter has internal switches that enable you to do this. |
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| Q |
I am using version 6.0 of AMS and I can only find 49 HART devices?
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| A |
There is a software bug in version 6.0 of the AMS Software that limits visibility to 49 devices. This bug has been fixed in versions above 6.0. Contact your local Emerson office or download the patch from the Emerson website. |
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| Q |
I have added a new HART device to my node but the IMS does not show it.
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| A |
When a new device is added, either a “loop rebuild” or a “reset” must be carried out to enable the new device to be seen in the IMS. |
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| Q |
I have performed a reset of the multiplexer but the LED’s on the MTL4842 appear to be scanning very slowly and it takes a very long time to finish the reset.
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| A |
The search mode on the MTL4841 has been selected incorrectly. There are three selections, Single Analog, Single Unknown and Multidrop.
The normal selection is “Single Analog”, this is selected if all of the HART devices have their addresses set to 0.
“Single Unknown” is used if the poll addresses of the devices are unknown. It will search each loop until it finds a HART device on any poll address, 0-15, as soon as it finds a device it will move to the next loop.
“Multidrop” is used where there are multiple devices on loops, this will search every poll address, i.e. 0-15, on every loop. |
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| Q |
I’m using Fisher Valvelink standalone software and AMS on the same node, but after connecting Fisher Valvelink I can’t see any HART devices under AMS.
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| A |
This problem arises because Fisher Standalone software automatically switches the MTL4841 mode from AMS to MTL when it connects. Unfortunately, when you connect back to AMS, the MTL4841 is in the wrong mode and AMS cannot restore the 4841 to AMS mode. The only advice that can be offered here is don’t use Fisher Valvelink standalone software on the same node as AMS. However, if the Fisher ValveLink software is used as a Snap-On within AMS, this problem will not arise. |
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| Q |
What value of terminating resistor should I use on the RS485 serial bus?
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| A |
The termination will normally be a simple resistive terminator with an impedance that matches the characteristic of the cable; this will normally be in the range 100-220 ohms.
RS485 interfaces should ideally be provided with a “matched” termination to prevent reflections and “ringing” of the signal on the bus cabling.
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| Q |
What are the maximum interconnection cable lengths?
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| A |
The maximum recommended length of 20 way HART ribbon cable between the BPHM64 backplane and the HART connection unit or IS backplane is 6 metres or 20 feet. Flat ribbon cables should not be taken outside the cabinet as they are not robust and susceptible to noise. Ground loops may also be an issue. If possible, locate the HART mux units close to the take-off points. For larger distances use more than one BPHM64 with MTL4841 modules fitted and link via the RS485 bus.
The maximum length of 10 way interface bus cable between a single MTL4841 communications module and up to 16 MTL4842 HART interface modules / backplanes is 4 metres or 13 feet, (between modules 1 and 16).
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| Q |
Can I remove the MTL4841 or MTL4842 or re-power the MTL4841 without interfering with the analogue 4-20mA signals?
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| A |
The MTL4841 and MTL4842 can both be removed or the MTL4841 re-powered without interfering with the analogue 4-20mA signal. |
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| Q |
When I perform a reset on my HART Device within AMS, the MTL4841 appears to reset then lock up.
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| A |
You are probably using a very early MTL4841 unit. This condition was corrected at software version 3.4. You should contact your local MTL representative for details on upgrading. |
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