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And here's a good article on why 3 wires are used for AC: http://amasci.com/amateur/whygnd.html

Have a look at this article: https://control.com/technical-articles/grounding-dc-power-supplies/

That would do it, 64-bit Windows can't run 16-bit applications. The Daniel Flow Computer likely uses a non-standard Modbus extension for accessing the floating point data, commonly referred to as Enron/Daniels Modbus. Refer to this thread for details...

Have you tried just running the old Wonderware IO server-Modbus application on your new Windows 10 64-bit computer? 64-bit Windows 10 can run 32-bit applications: https://docs.microsoft.com/en-us/windows/win32/winprog64/running-32-bit-applications

Well, to start, saying that the limitation is 32 "nodes" is not quite accurate. The limit is actually 32 "unit loads". While it's true that most older devices place 1 unit load on the RS-485 network, many devices today place a much smaller load, such as 1/2, 1/4, or 1/8 of a unit load. If all...

This is absolutely true and is an unfortunate part of the current state of Modbus devices. We've also had to make accommodations like these with our communication gateway and interface card products. The customer doesn't care that a device doesn't follow specifications, it just needs to work...

Is this the 'modpoll' you received from VP Instruments? https://www.modbusdriver.com/modpoll.html You should be able to get both modpoll and Modbus Poll to work using your USB to RS-485 converter - the flow meter can't distinguish between what's sending a request, so your configuration of...

It looks like VP Instruments has several flow meters. What's the model of your flow meter? How does the software interface connect to the flow meter? Does it use the RS-485 port or the USB port? Does it also communicate Modbus RTU to the flow meter?

Good idea to try writing to other registers and coils. It seems like you're doing everything correctly, and as you've seen, Modbus communications makes it appear that everything is working correctly, since you're getting valid responses back instead of exception responses. I think you need to...

Obvious question, but I need to ask anyway, have you power cycled the flow meter? Many devices need to be power cycled for any setting changes to take effect. Try a changing the baud rate, parity, and slave address on both your Modbus software and the flow meter, power cycle to the flow meter...

Timeout errors are typically caused by either incorrect wiring or mismatching configuration settings. Make sure you've connected the RS-485 +, RS-485 -, and 0V common signals of your USB to RS-485 converter to the flow meter. If your RS-485 converter or the flow meter supports 4-wire RS-485...

Make sure you are targeting the correct register. Some Modbus masters (such as ModScan) use 1-based addressing, while others (such as the MinimalModbus library) use 0-based addressing. For example, for the Set point, you would use 41 in ModScan, but use 40 in MinimalModbus (this assumes the...

Please do NOT use termination. Remove any termination resistors that may be connected to your devices or RS-485 cabling. Confirm that any built-in termination is disabled on all of your VFD's (i.e. the RJ45 port's pins 1 and 8 are NOT connected together) and your converter. Please use a USB to...

The Serial Communications section in the Commander SK Advanced User Guide is actually quite informative. Regarding termination, the manual states to connect pins 1 and 8 together on the RJ45 connector to apply the built-in 120 ohm termination resistor. Please make sure you have read and...

This register map seems wrong or perhaps this vendor's implementation of Modbus is incorrect. The text above the table states that data is stored in 2 16-bit registers (note that in Modbus each 16-bit register requires its own unique address), but the register addressing in the table only...

By ID, I assume you're referring to the Unit Identifier that is within the MBAP header. To answer your question, yes you could theoretically do this, but it would depend on the capabilities of the client. Also, you don't need to have both a different Unit Identifier and a different port...

Yes, you can use the same Ethernet connection for both PROFINET and Modbus/TCP devices. Our Ethernet gateways support multiple protocols simultaneously, which include both PROFINET and Modbus/TCP, and there are no issues with communicating using both at the same time. In fact, we have many...

You're correct, for Modbus RTU, the specification states the following: The entire message frame must be transmitted as a continuous stream of characters. If a silent interval of more than 1.5 character times occurs between two characters, the message frame is declared incomplete and should be...

Thank you for letting us know which library you're using. With the MinimalModbus library, it looks like you need to use the "read_long" function for 32-bit integers and "read_float " function for 32-bit floating point instead of "read_register"...

I believe you're correct, you need to read the 2 registers in a single Modbus request to read the 32-bit values from your slave device. If register 40200 has a 32-bit unsigned integer, you must read both 40200 and 40201 in a single request. This restriction is vendor-specific, but some devices...