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Electrical currents flowing through the medium can apply a voltage at the pH probe and affect the pH reading (which is a voltage reading). A battery powered portable might well have an isolation factor that an AC powered bench or process meter does not.

something or other Pressure Transmitter #1 something or other Pressure Transmitter #2

Happy New Year ! 1. Impulse tubing condensate leg. The manifold doesn't "go to the recorder", it connects to a differential pressure transmitter that senses the high and low pressures across a primary flow element and reports either the differential pressure, (DP) or the square-root extracted...

Even high end pressure transmitters typically do not have discrete output(s). Logic is typically done in the controller, not in the field device. Supposedly Foundation Fieldbus protocol could digitally talk to another output device on the same FF bus and give it an open or closed command...

In 2018, Modbus announced the release of specification for a Modbus Security Protocol. See the announcement here: https://modbus.org/docs/Modbus-SecurityPR-10-2018.pdf The announcement provides a link to 20 page security protocol spec, which requires acknowledging something or other to get to...

If you find out, please help out the Modbus community and let us know. Thus far, I've seen zilch (nothing) on implementation of Modbus security.

The correct bit patterns are not inverted, nor 2's complement. I suspect either - something is seriously wrong with your serial settings, baud rate, parity, stop bit, because none of the data makes sense at all. - the data stream is not Modbus The node address should be hex 01, not hex 7F...

You're on step 8 and I'm back on step 1 with your knowledge of programming techniques, of which I am ignorant. But I can tell you that the Modbus RTU frame over serial needs to be contiguous and it is very timing-sensitive, in contrast to Modbus ASCII over serial. When license-free...

Peak HMI slave simulator software uses 6 digit addressing as shown in the screen shot below: https://www.hmisys.com click on "Download" select "Peak HMI Slave Simulators links to "Slave Simulator Installer"

I had never noticed that Modpoll has the Enron/Daniel mode (64 bit) check box in the setup>read/write definitions group. Thanks for mentioning the Display>64-bit view.

My guess is that the value is a 64 bit integer (four, 16 bit Modbus registers) with the highest order register at 20480 and the lowest order register at 20483. Modpoll displays the 4 registers as - the value of the high order 32 bits in 20480/20481 as 0, - the value of the low order 32 bits...

You should only need I/O at site 2 (assuming PQF are the signals from site 2). The RTU should be able to communicate with a digital protocol to Site 2, without the need for the ? black box I/O at site 1. RTU should also be able to handle the field I/O.

Advantech has Remote I/O modules that handle 4-20mA input/outputs that talk Modbus/TCP in order to get the analog signal on an Ethernet bus talking Modbus. https://www.advantech.com/en/products/iot-ethernet-i-o-modules-adam-6000-6200/sub_gf-5197

For separate 232 or 485 functions, a google search comes up with all sorts of styles with screw terminal connections (your break-out style): short USB plug-ins, USB cable extended styles, DIN rail mount My criterion is for the brand name FTDI chipset because I've found it the most reliable...

To reiterate one of Jschulze's points: I've had issues with USB/serial converters communicating depending on whether the laptop was plugged into AC power or not. This kind of issue is why I like Ethernet over serial; Ethernet is, by design, isolated. I have to admit that I've run into exactly...

">don't be surprised to find there is very little use of deadband or hysteresis for COMPares for alarms--leading to LOTS of dithering Process Alarms" I'm curious. Can the deadband/hysteresis be adjusted or is that out-of-bounds?

Why are you insulating 'only', without a heat source? Has that worked in the past? Impulse lines are dead headed so there's no flow as a source from which heat can keep the impulse lines 'at temperature'. Heat conductivity through stainless steel is pretty poor, so any length of tubing...

There are diagnostic indicators in the transmitter’s digital display, symbols and characters, in addition to messages in the display. Check out the diagnostics troubleshooting section of the manual starting on page 74...

The back-up lithium battery in a holder in the CPU holds operating variables (not the main program, but operating variables). At ten years of age, it is likely to be dead. I'd start by replacing the back-up lithium battery. My experience shows that about 1/2 of all problems are power supply...

Try looking at another thread about Modbus connections. https://control.com/forums/threads/modbus-rtu-rs485.45155/ Note that RS-485 2-wire connections frequently are 'backwards' because of the inconsistent manner in which the driver lines are labeled by different manufacturers.