DanW

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About DanW

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  1. Presumably the reason for two pressure transmitters is that the tank is a closed vessel and there's pressure in the vapor space above the liquid. If you subtract the vapor pressure measured by the upper transmitter from the pressure measured by the lower transmitter (units have to be the same), convert the pressure value to a distance value (inches/feet,mm/m) and then divide the distance value by the Specific Gravity you will get physical level value. The problem with using two pressure transmitters instead a single differential pressure (DP) transmitter is that the combined error of both transmitters can be significant.   Convention calls for using a single DP transmitter.
  2. Thanks for the comments.  I have no exposure to robots and wondered what the real story was.
  3. High Pressure PID Control

    Does the valve/actuator assembly have a positioner?
  4. Serial comm is always a project, it is rarely plug-and-play.   You might need to make an adapter cable for the connection between the adapter in the field the RTU field device. You need to ring out the programming cable that you have to see which RS-232 function is on which pin, going from the laptop to the 'working' end and make a drawing of which pin goes where.  Make sure that the laptop's function match the adapter's functions on each pin.   Things can get reversed going from male to female, or counting from the wrong end.   When I've done stuff like that I always had a print-out of the make DB9 pinout numbering and the female DB9 pinout numbering. Then you need to match up the pinout on the other end to the RTU that is the field device so that the pin functions end up on the needed pins. You have noted that you need to use CAT 5 cable that is runs point-to-point between the two adapters.  This is NOT Ethernet and you can't connect the CAT cable to a switch, hub or router.
  5. The 50 feet limitation comes from the EIA specification.   It doesn't mean that the signal dies at 50 feet, but that one should expect reliable communications for installations 50 feet and under.  Performance beyond the stated limit can be compromised.  I know of two installations that when I arrived the RS-232 'cable' had already been installed, in one case about 65 feet, in the other about 75 feet away.   The 65 foot run was not even shielded, twisted pair, but it worked at 9600 baud and to my knowledge is still running today (commissioned in the early 2000's). On a similar note, Ethernet is rated to 100m.  A local town fair ran a CAT 5 cable 500 feet to get an internet connection that ran fine at 10Mb, back in the day before Wi-fi was everywhere (early 2000's).  The signal doesn't 'die' at the limit, but extending beyond the limit affects performance. My suggestion is to try comm with shielded twisted pair cables, at least 18g, 16g if you've got it to reduce any voltage drop.  As to converters, USB is more limited that RS-232,short cables only.   There are scads of 232/Ethernet converters.   There are Bluetooth/RS-232 converters but I have no experience at all with them.
  6. If the Modbus maps for the old unit and the new unit match identically, same register addresses, same data formats, and the serial settings on the replacement unit match the old unit, then the Modbus Master/Client should encounter not difference in either reading or writing data to/from new unit.   The assumption is that the operation of the new unit does not vary from the old unit, the commands work the same way, which is usually the case for updates over time because vendors want the replacment business and having functional compatibility between old and new Modbus comm tends to make people stay with the same brand.
  7. PiD Control question

    I'd guess V_SP" the setpoint with warm-up ramp with a value of 58?  Just guessing.
  8. Analog Input Module

    If the "RTD" in the part number of that input module means that that particular AI card is for direct connection of RTD's then the answer is most likely, "No, you cannot wire Infrared sensors directly to that card".  Nor are you able to take signal from the temperature controller because there is no known commercial temperature controller than outputs a resistance vs temperature signal.  The re-transmitting output of temperature controller is normally 4-20mA, sometimes a high level voltage, like 0-5V.  4-20mA and 0-5V is incompatible with a RTD input. The infrared sensor market has models that output 4-20mA over a specified temperature range and then there are models that output a non-linear thermocouple mV output over a temperature range.   The thermocouple output is designed to be compatible with thermocouple inputs but it is not compatible with an RTD input card. You need a different analog input card to handle an infrared sensor signal.
  9. You might try control.com and Plcs.net forums with this problem.
  10. Lesson Learned - Wonderware InTouch SCADA

    Nice write up, thanks.    Changes over time . . . .
  11. PID - large Integral value.

    Can’t comment on a value without knowing its units. Is P proportional band or gain? is I engineering units minutes or repeats per minute?
  12. Burn Therapy Chiller tank

    Have you investigated whether this qualifies as a 'medical device' that falls under the purview of the FDA?  I've seen far less ambitious projects at pharmas that were subject to testing, and FDA review and approval.   
  13. Discrepancy TCP modbus reading

    I did an HC-900 project back in 2010 or thereabouts.  That project used the standard fixed Modbus map, not the user-defined custom Modbus map. I do recall that Honeywell sold a large project in Europe at which point they discovered that Modbus did not work very well and produced several CPU firmware updates with Modbus revisions, 2010 or earlier.  So one question is, how old is this HC-900?  Could it be from the early period when there were Modbus bugs? Do you know if the Modbus register ever reported current values instead of stale, out-of-date values or is this the first time anyone's discovered it? If you can see the variable changing monitor mode in Control Designer, then I suspect that it is a mapping problem.  Somewhere in the presentation it describes how to print or export the Modbus map so you can check which tags are at which Modbus address. I attempted to upload a 1.5Mb pdf version of Honeywell power point on Modbus training for the HC-900 but the forum doesn't like it and I doubt there's a reasonable solution. The details in my memory are long gone on specifics of navigating HCD software, so I can't really help you, but if you post a throw-away email address that can handle an attachment, I'll email the training pdf to you.
  14. The vendor reached out and said the displays arent calibrated only the output signal is Just a rant.  I've run into this on other instrumentation and it amazes me that a digital value for the measured process variable is available internally, so why isn't the digital display displaying the digital value and not converting an analog value?  You'd think that you could trust the local display as having the highest integrity as the representation of what's being measured, but no, the analog output is calibrated, not the display.  
  15. 1746-NT8

    I've  never used a 1746-NT8, but my reading of the 1746-NT8 manual says that it should theoretically cover the range -454°F through 2498°F. The blinking green channel LED indicates an over range input at the mV generated by whatever you're using to simulate 2498°F.  The fact that when you back the simulator off to 2488°F indicates to me a calibration issue: whatever the simulator is putting out the module interprets as the top of the A/D range: 32,757 counts at what thinks is should be 2488°F.   The top of the A/D range, 32,757 counts should be interpreted as 2498°F, not 2488°F.   I think you need to calibrate the input so that the module indicates 2498°F when the simulator provides the mV at 32,757 counts. As to the practicality of using Type K's above 2300°F (or below -30°C), or other upper levels, there's lots of bar stool opinions by long term users.   The 2498°F top value for Type K comes from the NIST tables (1370°C).   Many, many vendors have a lower limit on their Type K's based on reality experiences.   Honeywell's HC-900 thermal PAC ranges a Type K only up to 2192°F (1200°C).   Type K's can exhibit a fairly short 'valid' life at the high end of NIST table.   The problem is that the thermocouple can drift, which happens much more rapidly at high temperatures, and if the element does not break open, the T/C card still 'sees' a mV signal, but since the thermocouple has drifted the temperature calculated for the mV signal is false.  There is no way to compensate for drift.   You don't know how much or in what direction the drift is, because the T/C still appears valid because it's not an open circuit (it's not a thermocouple break condition).