Remote SP problem with Eurotherm 3216

Hello
I have an Eurotherm 3216 with remote SP input on terminals HF and HD. It is 0-5 Volt DC.
When I look in Conf-SP-Rem.sp I see the actual value of remote SP. And it works well here. At 5 Volt remote SP the reading here is 100. But the home display lower line, which shows the SP, always shows 0,8 to 0,9, regardless if the remote setpoint is 1 or 5 Volt. Only if the remote SP is less than 0.1 Volt, the indicated SP in Home display shows 0.0.
What is wrong?
Regards Finn
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  • Jon (Official Rep) February 13, 2013 16:27
    Hello Finn,
    To see the remote setpoint on the home screen you have to select 'Yes' to the 'L-R' parameter in the SP list - Has this been done?
    Regards, Jon
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  • When I switch off remote SP (on digital input LA) then the normal SP1 is correct shown on Home lower line. But as written: with remote SP the lower line in Home shows 0.8 to 0.9 for all voltages above 0.1 Volt DC.
    Finn
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  • Usually this would indicate that the remote setpoint scaling on the 3200 is set wrong. There are two parameters in the SP list in config mode that set the scaling of the remote input, which are REM.HI and REM.LO respectively.

    From memory (I wrote the software in the 3200, but this was some years ago!) these set the values of the setpoint at 0 and 10 volts respectively, so you have to extend the REM.HI by interpolating what you want to be the full scale value at the 5V point.

    One other thing the instrument does is to clip the remote setpoint within the overall setpoint limits, so if the SP.HI and SP.LO are set wrong they can affect the value. From the other things you say this is unlikely as you're able to set the non remote setpoint to a correct value.

    The other possibility is incorrect calibration of the remote input. This is unlikely as the units are fully calibrated and tested in the factory. It is possible to do a calibration of the remote input, but to be honest if it's wrong, the best thing to do is to get it recalibrated via service, assuming you're under warranty.

    And finally the 4-20mA input on HE would override the HF voltage input, so if there is anything connected to that terminal disconnect it (very very unlikely).

    If you get stuck, the best thing to do is to note down all the settings in the SP list and send them in.
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  • The process input scaling is 0-200.
    SP.HI = 200
    SP.LO=0
    There is no input on HE(no wire connected).

    The mentioned observations in my first posting, were with
    REM.HI=200
    REM.LO=0

    If I change REM.HI to 1000 or 10 I have exactly the same observation:
    With remote SP the lower line in Home shows 0.8 to 0.9 for all voltages above 0.1 Volt DC. With SP1 active, the lower Home line shows the SP1 correct.

    Note: I was wrong about the remote input, it is 0-10 VDC,(not 0-5 VDC) which can be seen in REM.SP which shows the actual scaled remote input.

    Here are the SP settings, with remote SP scaled to 200:
    SP.SEL=SP1
    SP1=11.0
    SP2=0
    SP.HI=200
    SP.LO=0
    REM.SP=200 (with 10.0 VDC on remote SP)
    L-R=Yes
    SPR.AT=200
    REM.PV=m Ln
    LOC.T=010
    REM.HI=200
    REM.LO=0
    ROP.HI=100
    ROP.LO=0

    Finn
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  • I just noticed another thing:
    When in remote the "Run" lights all the time.
    It indicates that the SPR.AT=200 can not ramp to the remote SP.
    When I switch to local SP the Run light for some seconds while the SP is ramping.

    I set the SPR.AT to Off, and voila, the remote SP is shown correct on Home lower line.
    My conclusion: There is some internal problem with calculating between local SP ramp and remote SP ramp.

    Finn
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  • Sorry for the slow response, I have been out of the office.

    I understand you are saying that the REM.SP is showing the "correct" setpoint value, scaled between 0-10V and 0-200.

    I think you are right that there is some interaction between the setpoint ramp function and the remote setpoint. What is possibly happening is that noise on the DC input is causing the instrument to believe it has a new setpoint and starting a new ramp, so in effect the setpoint locks at the first step of the ramp (it is continually restarting the ramp).

    I've never seen this problem before, so this is hypothetical, but it seems to fit the symptoms. I'll have a look and get back to you.
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  • Can you tell me what the instrument is displaying for measured value of the main input while this is happening? My first analysis does seem to show a potential problem as I suggested, but I've asked someone to set up and double check.

    Excellent information on the problem report, by the way, very helpful piece of diagnosis.
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  • Finn, apologies for not getting back sooner.

    The RSP behaviour is not as expected and we've raised an internal investigation ticket to look in more detail.

    Could you please send an email address/phone number to me at tim.linnell@invensys,com - it will be necessary for our support people to talk to you to find an interim workaround.
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  • While investigating this problem I appear to have found a work-around:

    The crux of the problem is that the Working SP does not reflect the Remote SP when the SP Rate is set to anything other than OFF.

    It appears that setting the TIMER to DWEL or PROG will allow the WSP to show the RSP as required.
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  • Thanks, Tim and Trevor

    Because I in the meantime have got some 3216 with RS485 I decided to change the input card from analog renote SP to RS485. So I am not able to test your solution.

    But again, thank you for the answers.

    Finn
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