DanW

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About DanW

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    instrument guy

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  1. How should I matching the impedance?

    There’s all those status bits, channel enable or input type selection that affect card operation.   With respect to impedance matching, if the device AO is a standard commercial 4-20mA output, then its output impedance is what it is and is presimably rated to be capable of driving 21mA of DC current through a reasonable load resistance, typically a minimum of at least 500 ohms, sometimes as much as 750-1,000 ohms for AC powered devices.   Unless the copper wiring is excessively long and small diameter (high resistance), any 4-20 mA loop driving a 250 ohm input resistance should  work OK.   There is no impedance to ’match’; the total loop resistance just has to be lower than the maximum load resistance the AO can drive (spec’d somewhere in the spec sheet). The installation guide shows the ”I in 0-” terminal jumpered to the ”ANLG Com” terminal for loop powered transmitters.   I’d probably try a temporary jumper to see if it makes any difference.   The warning about voltages on V/Iin+ and Iin+ having to be plus/minus 10Vdc is valid; that’s the common mode limitation for this module.   If the device ground is more than 10v from the AI card ground, the 4-20mA current signal disappears in resulting ground loop, which may be happening.   Ground loops between a single ended, non-isolated analog output and an AI are quite common.
  2. How should I matching the impedance?

    Sure you wired it right? Is it a loop powered transmitter?  Have you wired a DC power supply into the loop? 
  3. Ultrasonic Flow Meter noise

    Are the Flowmeters AC or DC powered? Some frequency outputs are passive that need loop power to operate. If a 24Vdc power supply is in the frequency loop, is the 24V common grounded or floating?   Can you ground the DC supply if floating, or float it if it is grounded in order check alternative performance? I have heard of some field instrument outputs picking up noise from switching DC power supplies, where the solution was to substitute a linear DC power supply.   Linear supplies are now uncommon, but it might be worth the effort to locate one for testing to see if it makes any difference. Presumably the Fluke is battery powered and floating.     Are the frequency test results done with the field wires disconnected from the input terminals of the AB input card, or with the field wires connected? I wonder what an AC powered, grounded chassis oscilloscope would show for an ”as connected” test (in parallel with the connected field wiring)? I’ve seen 4-20mA common mode issues disappear when the field wiring is disconnected and its signal checked with a floating battery powered meter where problem reasserts itself when the field wiring is re-connected, because common mode is ’common’ between two points - remove the commonality (wiring connected, not floating) and the common mode disappears. Try the same frequency test with the (-) low side meter probe grounded to see if you get the same results. 
  4. Help with PLC communication basics

    PLC’s basically run ’real-time’ and do not routinely store data unless specifically programmed to do so.   ’HMI software’ (several flavors listed in the post above this one) takes on the task of communicating with the PLC to get data from or to write data to the PLC. As someone noted, some PLC comm ports are for programming, others for data transfer; depends on app specifics.    It takes a ’driver’ to talk to a specific brand/model PLC.   OPC server (Windows software) are like a gateway; one side has a driver that talks to the  PLC, the other side exchanges the data from the PLC with an OPC client.   OPC clients are built into most HMI software packages nowadays.  The latest iteration of OPC, OPC UA, is friendly on the server-client side, listing PLC configured tags in the client, but the driver side still requires ’building a tag database’ for many devices.   I think the proposed task is incredibly ambitious.  I find the prospect of connecting to a variety of installed controllers daunting, to say the least.   It’s my opinion that the world of IIoT is largely an illusion with its implementations requiring significant programming effort. Best of luck in the endeavor.        
  5. Banner DXM 700 or other Model

    I have configured dozens of DX80 gateways over the years, mostly mapping AI’s to AO’s, DI’s to DO’s.  It was straight forward with the software. Then came the DXM100.   I bought one to try and after a day’s effort at trying to get the DXM onboard AO to ’follow’ the node radio AI, I gave up.   The factory, which used to have superb support, blew me off.  The DXM100 was supposed to offer cellular communications and my guess is that Banner packed a whole bunch of programming features into it that the DX80’s did not have, especially in light of their marketing push into the agriculture markets (irrigation, soil moisture).  In that move, they made a gateway that won’t handle a 4-20.   Good for them. I didn’t bother to compare the DXM100 vs the DXM700 and I couldn’t find an on-line comparison chart.   Out of curiosity, why does yourclient want a particular brand/model wireless gateway?
  6. FX5U Modbus communication

    Historically and generally, a spec for the maximum number of units on an RS-485 network is based on the RS-485 chip in the device, and the frequently followed by the disclaimer (as in embedded graphic in the first post above) like "the number of slaves varies depending on communication equipment type". There have been advances in the 3+ decades that RS=485 has been around, and there are 485 chips that can support 64 devices, but the entire network has to be those chips. The Modbus RTU protocol limit for addressable slaves is 247 slaves. 
  7. FX5U Modbus communication

    A couple comments about Modbus in general. 1.  Consider how often the master can communicate with each slave.  The query/reply time period for multiple slaves adds up.   If one slave is “down” then the master waits for that slave’s reply until the master “times out”.  Consider a relatively workable means of de-selecting slave(s) in the master’s polling list should a slave be out-of-service. 2.  Pushing the maximum number of nodes on a single network/bus frequently leads to communications issues where a simple work-around is to use an RS-485 isolator repeater half way down the bus so the 485 drivers do not have to drive all the loads, only half the total loads.  
  8. Rules for the Forum

    As a non-admin, but long time forum participant on multiple industrial controls fora, my observation is that attempts to produce better interaction by establishing ’rules’ is not going to go anywhere. The fact that many OP’s never return-post beyond their initial post is universal. The fact that most OP’s do not clearly articulate their problem and leave out critical information is universal. The fact that some people desperately ’want’ something that is not commercially available is universal.   The fact that there is continued belief in one-size-fits-all ’secret PID terms’ that somehow just are not published but will be revealed in a forum thread is and will be universal. The fact that about 70% of my replies come straight out of a publicly available (downloadable from the web) manual or spec sheet will not inhibit those who will not research their own topic themselves. Just like the saying, ”there are 10 kinds of people, those understand binary and those who don’t”, there are those who understand troubleshooting and those who don’t.   I fail to understand those who stay in a vocational field where the ability to troubleshoot is ubiquitous, but hey, it’s their problem. Make up all the rules you want to, but just like I don’t bother to read EULA’s, they won’t bother to read or pay attention to new rules. my 2 cents
  9. ProfiBus Noise

    Try this article by a SMAR engineer http://www.smar.com/en/technical-article/tips-for-trouble-shooting-on-the-profibus-dp Other technical articles not specific to Profibus on that site, too Or this one: https://procentec.com/about/news/2016/a-short-guide-to-addressing-emc-on-profibus/
  10. Analog Wiring NO NO

    OK.  I thought the distinction your were making was signal type (analog vs digital), not connector type (screw terminal vs terminal block).   Even so, given the number of times I've found the problem to be a whisker (that errant single strand) that makes it way out from under the screw terminal and touches where it shouldn't, I'd take a ferrule over bare stranded wire even if a fork is the correct and proper solution.   Have you encountered maintenance/performance-over-time issues with ferrules under screw terminals?n   Loosening?
  11. Analog Wiring NO NO

    I have the panel shop use twisted pair from the short run from field terminal blocks to the AI cards.  You can see the blk/clear pair below coming up from the top of the field terminal blocks. I haven't a clue why analog signals rate fork terminals and discretes rate ferrules.  What's the logic for that?
  12. Universal Analog Input Card

    It is not just a marketing term, there is a true functional difference between a dedicated function analog input card (4-20mA only) and a universal input card. An analog input card that takes a direct RTD or thermocouple input in addition to 0-10Vdc and 4-20mA has a lot of functionality that an analog input card that a 4-20mA-only card does not have.
  13. Honeywell HC900

      1.  Did the HMI ever communicate successfully with the CPU, or is this a commissioning/start-up problem? 2.  What HMI instruction faults the HC900 CPU? 3.  Which version firmware is the HC900 CPU running? 4.  Which hardware comm is for CPU/HMI comm?  Ethernet or RS-485? 5.  Is the HMI the Modbus Master, HC the Modbus slave? 6.  Are the CPU’s genuine Honeywell, or the fake, knock-off made in India models?
  14. Swimming Pool PLC

    If the pump doesn't pump water or the heater doesn't turn on and heat, then you need to determine whether the pump or heater is faulty or whether the control circuit that tells the pump to run or the heater to turn on can be the reason those things do not turn on and do what they're supposed to.  
  15. What performance factor is so critical that you'll travel 1/3 way around the world to find an alternative to what you're using now?  What does your current vendor suggest for upgraded performance? In answer to your question, I'm unaware of any standard of comparison.  But I can understand why - so much of PLC's performance is related to how it is programmed.