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Search: Posts Made By: Tom Jenkins
Forum: LIVE PLC Questions And Answers October 10th, 2018, 03:28 PM
Replies: 10
Views: 494
Posted By Tom Jenkins
There are limited bits of info you can get...

There are limited bits of info you can get without documentation. The documentation is needed for final verification of everything.

First, Ethernet is not a protocol, it is a transmission method....
Forum: LIVE PLC Questions And Answers October 9th, 2018, 02:58 PM
Replies: 37
Views: 1,415
Posted By Tom Jenkins
A clarification is required. Voltage rating...

A clarification is required.

Voltage rating identifies the voltage difference between a device or wire that can be withstood before an arc will jump, plus, of course, a factor of safety. Any...
Forum: LIVE PLC Questions And Answers October 5th, 2018, 05:44 PM
Replies: 13
Views: 476
Posted By Tom Jenkins
Hazardous area design requirements get pretty...

Hazardous area design requirements get pretty obscure at times.

A common occurrence in wastewater treatment plants is the call for all explosion proof light fixtures and panels in digester areas....
Forum: LIVE PLC Questions And Answers October 3rd, 2018, 04:56 PM
Replies: 11
Views: 489
Posted By Tom Jenkins
If you contact the publications you are...

If you contact the publications you are interested in and indicate your interest they will send you a guide that indicates rates, numbers of subscribers, geographic areas covered, target readership,...
Forum: LIVE PLC Questions And Answers October 3rd, 2018, 04:36 PM
Replies: 9
Views: 406
Posted By Tom Jenkins
HMI requirements - color, screen size, etc. ...

HMI requirements - color, screen size, etc.
Selector switches, pilot lights, pushbuttons, manual override requirements
Communications requirements for SCADA, protocols, etc.
Customer preferred PLC...
Forum: LIVE PLC Questions And Answers October 1st, 2018, 04:21 PM
Replies: 7
Views: 279
Posted By Tom Jenkins
Let's assume three identical pumps. You need...

Let's assume three identical pumps.

You need to know the flow. This can ideally be measured, but if necessary it calculated from pump performance curves based on pressure. If flow can't be...
Forum: LIVE PLC Questions And Answers September 30th, 2018, 10:30 AM
Replies: 27
Views: 747
Posted By Tom Jenkins
You are quite welcome. For those not used to...

You are quite welcome.

For those not used to using the trendline method, it can be a bit tricky getting more decimal places to display. As Mispeld indicates, the default display is inadequate.
...
Forum: LIVE PLC Questions And Answers September 28th, 2018, 05:24 PM
Replies: 27
Views: 747
Posted By Tom Jenkins
If your NH3 transmitter is accurate to 0.1% of...

If your NH3 transmitter is accurate to 0.1% of Full Scale, a third order polynomial will calculate as accurately as you can measure. Fourth order will calculate more accurately than the measurement....
Forum: LIVE PLC Questions And Answers September 28th, 2018, 04:07 PM
Replies: 27
Views: 747
Posted By Tom Jenkins
I usually express the residual as percent error....

I usually express the residual as percent error. That helps put it in context.
Forum: LIVE PLC Questions And Answers September 28th, 2018, 02:44 PM
Replies: 27
Views: 747
Posted By Tom Jenkins
I agree with Peter. When you develop a...

I agree with Peter.

When you develop a polynomial in Excel (or many other regression methods) you can select the order of polynomial. I've found that third or fourth order will accurately model...
Forum: LIVE PLC Questions And Answers September 27th, 2018, 01:57 PM
Replies: 5
Views: 358
Posted By Tom Jenkins
If the signals are discrete and not analog there...

If the signals are discrete and not analog there shouldn't be a problem.
Forum: LIVE PLC Questions And Answers September 26th, 2018, 10:00 AM
Replies: 12
Views: 786
Posted By Tom Jenkins
Very neat site!

Very neat site!
Forum: LIVE PLC Questions And Answers September 25th, 2018, 09:36 AM
Replies: 12
Views: 786
Posted By Tom Jenkins
Very Interesting Book

This new text has a lot of info. We get a lot of newbies here. This is a great starting reference. And, it's free.
...
Forum: LIVE PLC Questions And Answers September 24th, 2018, 08:20 AM
Replies: 8
Views: 407
Posted By Tom Jenkins
Stepper motors are used when accurate control of...

Stepper motors are used when accurate control of position and speed are important.

The applications for VFDs you mention are based on control of speed, and precise control of speed isn't required....
Forum: LIVE PLC Questions And Answers September 17th, 2018, 02:53 PM
Replies: 4
Views: 429
Posted By Tom Jenkins
pH control is very non-linear. It is tough to...

pH control is very non-linear. It is tough to control with PID, as Zlinger suggests. I would consider using floating control, with different steps in the dosage at different pH levels.

I don't see...
Forum: LIVE PLC Questions And Answers September 13th, 2018, 09:33 AM
Replies: 34
Views: 1,708
Posted By Tom Jenkins
I'm not an expert, and I don't want to be. The...

I'm not an expert, and I don't want to be. The arc flash can occur anytime, but it's effects are most hazardous when the enclosure is open and personnel are in close proximity. I don't know how much...
Forum: LIVE PLC Questions And Answers September 13th, 2018, 08:13 AM
Replies: 34
Views: 1,708
Posted By Tom Jenkins
Initially, the insurance carriers discovered that...

Initially, the insurance carriers discovered that the bozos running uninsulated wire around houses, supported by nails, were causing fires. That led to UL. Then the carriers discovered people were...
Forum: LIVE PLC Questions And Answers September 12th, 2018, 09:41 AM
Replies: 11
Views: 525
Posted By Tom Jenkins
In addition to the problem with power and torque...

In addition to the problem with power and torque mentioned above, there is a limit on motor speed due to the centrifugal force on the rotor and the lubrication and speed limits of bearings. Typical...
Forum: LIVE PLC Questions And Answers September 11th, 2018, 11:01 AM
Replies: 16
Views: 664
Posted By Tom Jenkins
Regardless of the solution, you should consider...

Regardless of the solution, you should consider winding RTDs or other motor temperature monitoring system. The frequent starts of the conveyor will draw high current, even with a mechanical clutch,...
Forum: LIVE PLC Questions And Answers September 10th, 2018, 10:54 AM
Replies: 34
Views: 1,708
Posted By Tom Jenkins
I also agree with Paully's recommendations. Cost...

I also agree with Paully's recommendations. Cost and space savings from common enclosures are usually offset by the arc flash issues. You can expect insurance carriers to start getting nasty about...
Forum: LIVE PLC Questions And Answers August 30th, 2018, 09:19 AM
Replies: 10
Views: 502
Posted By Tom Jenkins
The First Law of Thermodynamics is inviolable. If...

The First Law of Thermodynamics is inviolable. If you want twice the force and twice the distance you need four times the energy input.

Your second post contradicts your first. Get a grip on your...
Forum: LIVE PLC Questions And Answers August 23rd, 2018, 02:08 PM
Replies: 6
Views: 685
Posted By Tom Jenkins
With a long lag time I suggest you consider...

With a long lag time I suggest you consider floating control. You could put a time delay between loop executions.
Forum: LIVE PLC Questions And Answers August 21st, 2018, 10:40 AM
Replies: 7
Views: 497
Posted By Tom Jenkins
I generally fuse the signal lines to remote field...

I generally fuse the signal lines to remote field transmitters. Fusing, or circuit breakers, on the power supply itself should be sufficient. I don't see an advantage for protecting each conditioner...
Forum: LIVE PLC Questions And Answers August 14th, 2018, 09:32 AM
Replies: 10
Views: 386
Posted By Tom Jenkins
You are correct in saying that almost all flow...

You are correct in saying that almost all flow sensors measure velocity. About the only exception is the positive displacement meters used for liquids in custody transfer - for example, the water...
Forum: LIVE PLC Questions And Answers August 1st, 2018, 11:49 AM
Replies: 5
Views: 314
Posted By Tom Jenkins
Yes, but you need an ISP, an Ethernet Port, and...

Yes, but you need an ISP, an Ethernet Port, and software on the RTU to format the data, and/or software on the cloud to poll the RTU or accept the data pushed to the cloud. The most common approach...
Showing results 1 to 25 of 500

 
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