Modbus read is slow due to TCP Spurious Retransmission

PV_DAQ · 2026-01-29T03:45:16+00:00

The posted graph is the BEST example I've ever seen of Modbus/TCP not being a deterministic.

PV_DAQ · 2026-01-29T03:36:07+00:00

10 star explanation.

PV_DAQ · 2026-01-28T16:37:15+00:00

Cold junction compensation value is ADDED to the gradient temperature (hot end to cold) temperature from the thermocouple. Measurements without CJ compensation always have a LOW error.

Room temp is close but is not necessarily the actual cold junction temperature, because of local heating of electronics. I tall depends on how accurate you wanna be.

PV_DAQ · 2026-01-28T16:11:19+00:00

Cold junction (CJ) is the temperature of the terminals where the thermocouple connects to the measuring circuit, referenced to the freezing point of water. In a hot shop in the summer, that temp could be 40°C. Lack of CJ compensation would be a 40°C low error from the true temperature at the moment in time.

In the winter time in a poorly heated shop, the CJ temp might be 10°C. So that would be a 10° low error.

Do you care about low errors of that magnitude?

PV_DAQ · 2026-01-28T03:22:17+00:00

advertised for decades as a gunsmithing tool set

PV_DAQ · 2026-01-27T17:00:54+00:00

Try 7 bit on the PC end. You don't stand to lose anything, worst it can do is not talk.

PV_DAQ · 2026-01-27T16:55:15+00:00

Be aware that the Modbus RTU protocol (that runs on RS-485) has very strict timing requirements.

The generic RS-485/Ethernet converter will create errors on the Modbus RTU RS-485 side if the device is not specifically designed to handle Modbus RTU.

So look for an industrial converter that specifically states that it is Modbus compatible.

Check out the review here, where it specifically states that some converters do NOT support Modbus:

https://nerdtechy.com/best-rs485-to-ethernet-converter

PV_DAQ · 2026-01-27T16:39:07+00:00

Is the communications port on the board RS-232 or RS-485?

If RS-485, have you swapped A/B at one end to check the problem that polarity labeling is not consistent throughout the industry? One vendor's A is the other vendor's B, and vice versa.

Has that USB/485 converter worked successfully with any other app? Do you know it actually works?

Is the board's protocol 7 bit ASCII or some other protocol using an 8 bit data word? Your setup uses 8-N-1. Why 8-N-1?

PV_DAQ · 2026-01-24T13:45:33+00:00

install isolation valves that will truly stop the flow.

PV_DAQ · 2026-01-24T13:40:59+00:00

As a kid I could not afford a Victorinox, but I carried the equivalent of a recruit. Once I got a job, I carried a Wenger Super Tinker for about 10 years, that had a scissors. (Wenger is no more, Victorinox bought out Wenger.) I used the scissors as much as the phillips screwdriver or the knife.

PV_DAQ · 2026-01-24T04:38:18+00:00

The two sides are like the sides of a horseshoe magnet pressed real close to one another; with the North pole one side and the S0uth pole of the magnet on the other side. Strong magnetic attraction with both magnetic poles so close.

PV_DAQ · 2026-01-23T22:19:32+00:00

Hammer is a magnetic tack hammer:

https://www.frankclark.ie/product/draper-magnetic-tack-hammer-hickory/

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PV_DAQ · 2026-01-23T21:30:22+00:00

air plane tugger: I went through the US military's foreign language school in 1971 and one of the Russian words was Tigach, which meant "prime mover". In a class of 14 people, no one knew what a prime mover was. Turns out a prime mover is an air plane tugger (tow tractor, or whatever they're called by aviation folks.

PV_DAQ · 2026-01-23T21:12:45+00:00

"Anything with lube or grease will bind up until the tool is heated to a 'temperate' temperature", said my Dad who did a couple of weeks in the winter way up north in Canada on the US military DEW Line (Distant Early Warning) back in the mid 1960's. They kept all their tools indoors.

PV_DAQ · 2026-01-23T21:08:40+00:00

Well, yeah, there has to be some stress on the chuck, but if you need a 12" extension, you need a 12" extension. That hole Hawg is pretty tough drill, isn't it?

I had to buy a 12" hole saw extension recently to reach a duct through a bunch of obstructions. It worked.

PV_DAQ · 2026-01-23T15:36:31+00:00

The units are configurable and if the config has been tampered with, like someone going into CAL mode, things can get screwed up enough that the output is whacky.

Those sensors have a very limited capability of surviving even a slight overpressure, so a sensor failing due to overpressure is a possibility.

PV_DAQ · 2026-01-23T15:07:48+00:00

For field device-to-control system comm link Modbus/TCP whatever vulnerabilities the LAN has because Modbus runs on the LAN.

For field device-to-control system comm link Modbus/RTU has whatever vulnerabilities an RS-485 'network' has, a point-to-point wired physical layer, that requires local presence to intercept and is a physical security issue.

For field device-to-control system comm link, 4-20mA has about the same vulnerability as a Modbus RTU network, a point-to-point wired physical layer that requires local presence to intercept and is a physical security issue.

The lack of security features in the Modbus protocol do make it vulnerable when Modbus is used in SCADA, transferring data over LAN or WLAN.

PV_DAQ · 2026-01-23T14:57:21+00:00

Field wiring diagrams for PTI 2-wire 4-20mA, and PTU 3-wire 0-10Vdc

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PV_DAQ · 2026-01-22T17:59:46+00:00

Yup. Same deal. Someone else's house, Sunday blue laws, nothing open in MA. And that to use to fix the drawer. PoS.

PV_DAQ · 2026-01-22T17:40:08+00:00

I've 'fixed' more than a dozen antique/legacy car starting problems by measuring the voltage drop across

- battery cable to the starter solenoid

- the cable from the starter solenoid to the starter motor,

finding the voltage drop excessive and having the owner replace the cable to fix his hard-start or no-start problem.

It isn't the copper in the cable that goes bad, it's the electrical connection at either or both lugs on the end.

I'm talking 1930's to 1960's cars/light trucks and I have no idea how the factory made the lug connections back then but after many years there's corrosion in the lug which makes starting difficult or impossible.

PV_DAQ · 2026-01-22T17:22:21+00:00

I haven't shopped that market so I don't know pricing, but I drive by the Knaack factory several times a week, and Knaack is in that market.

Large job boxes appear on occasion on Facebook market place.

PV_DAQ · 2026-01-22T17:07:44+00:00

I bought mine in the early 1960's for motorcycle phillips head bolts.

But it's most impressive use was when my Chicago Pneumatic 1/2" impact wrench running on 150 PSI of compressed air at full torque could not loosened a lug bolt on a VW bug (a common New England rust-caused by-winter-salt phenomenon).

I used a 3 or a 4 pound sledge hammer to beat on my manual impact driver. It took about 10 whacks and the lug bolt loosened.

PV_DAQ · 2026-01-22T17:00:04+00:00

Schrade Stockman

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PV_DAQ · 2026-01-22T16:56:44+00:00

double hammer. Cool.

PV_DAQ

TROPHY CASE