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Search: Posts Made By: Tom Jenkins
Forum: LIVE PLC Questions And Answers Today, 11:55 AM
Replies: 15
Views: 401
Posted By Tom Jenkins
Mutual misinterpretation, I guess - no problem. ...

Mutual misinterpretation, I guess - no problem.

I always start with the load by figuring torque and horsepower. Then I work backward to the motor demand. Then, whether there is a mechanical speed...
Forum: LIVE PLC Questions And Answers November 16th, 2018, 05:29 PM
Replies: 15
Views: 401
Posted By Tom Jenkins
No, it is not. The only place that violates...

No, it is not.

The only place that violates the First Law is a nuclear reaction, and that is governed by e=mc˛.

The equation for torque vs. hp and speed still applies. The power into the VFD...
Forum: LIVE PLC Questions And Answers November 16th, 2018, 02:02 PM
Replies: 15
Views: 401
Posted By Tom Jenkins
First LAW of Thermodynamics: Energy is not...

First LAW of Thermodynamics: Energy is not created or destroyed.

Power is energy per unit time.

Therefore the horsepower throughout your system is always the same, minus losses to friction, of...
Forum: LIVE PLC Questions And Answers November 15th, 2018, 03:23 PM
Replies: 19
Views: 631
Posted By Tom Jenkins
True enough. This happened to be a plot I found...

True enough. This happened to be a plot I found while looking for something else.

I guess you'll just have to take my word for the fact that the amps/flow were controlled to the set tolerance,...
Forum: LIVE PLC Questions And Answers November 15th, 2018, 12:47 PM
Replies: 19
Views: 631
Posted By Tom Jenkins
Here is an example of floating control on an...

Here is an example of floating control on an inlet throttled blower. Amps are proportional to air flow.The application was dissolved oxygen (DO) control of a variable level sequencing batch reactor...
Forum: LIVE PLC Questions And Answers November 15th, 2018, 08:43 AM
Replies: 19
Views: 631
Posted By Tom Jenkins
The attached may help. I don't have a ladder...

The attached may help. I don't have a ladder logic example handy, but if you need it after looking at these illustrations I can put one together.

You can make the control fast or slow by changing...
Forum: LIVE PLC Questions And Answers November 14th, 2018, 01:36 PM
Replies: 19
Views: 631
Posted By Tom Jenkins
My preferred technique is floating control. By...

My preferred technique is floating control. By including time delays for response and a dead band for stability I find it more responsive than PI or PID and less prone to hunting.
Forum: LIVE PLC Questions And Answers November 2nd, 2018, 09:59 AM
Replies: 30
Views: 1,255
Posted By Tom Jenkins
Pump flow varies directly proportional to speed....

Pump flow varies directly proportional to speed. Pump discharge head varies with the square of the speed. The relationships are known as the affinity laws.
...
Forum: LIVE PLC Questions And Answers October 31st, 2018, 11:27 AM
Replies: 44
Views: 1,584
Posted By Tom Jenkins
100% agree. "Normal" in the context of...

100% agree.

"Normal" in the context of contact status has NOTHING to do with the status of the contact during so-called normal operation.
Forum: LIVE PLC Questions And Answers October 22nd, 2018, 10:13 AM
Replies: 9
Views: 316
Posted By Tom Jenkins
I hear that a lot, but that is really less often...

I hear that a lot, but that is really less often a problem than it is usually thought to be.

Let's say your PLC input impedance is 150 k-Ohm. At 10 VDC the current is only going to be 67...
Forum: LIVE PLC Questions And Answers October 22nd, 2018, 08:28 AM
Replies: 9
Views: 316
Posted By Tom Jenkins
Another advantage of 4-20 mA transmitters is the...

Another advantage of 4-20 mA transmitters is the availability of many in 2-wire loop powered configurations. Voltage outputs are 3-wire or 4-wire.
Forum: LIVE PLC Questions And Answers October 10th, 2018, 04:28 PM
Replies: 10
Views: 536
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, 03:58 PM
Replies: 37
Views: 1,567
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, 06:44 PM
Replies: 13
Views: 552
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, 05:56 PM
Replies: 11
Views: 603
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, 05:36 PM
Replies: 9
Views: 473
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, 05:21 PM
Replies: 7
Views: 340
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, 11:30 AM
Replies: 27
Views: 849
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, 06:24 PM
Replies: 27
Views: 849
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, 05:07 PM
Replies: 27
Views: 849
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, 03:44 PM
Replies: 27
Views: 849
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, 02:57 PM
Replies: 5
Views: 389
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, 11:00 AM
Replies: 12
Views: 846
Posted By Tom Jenkins
Very neat site!

Very neat site!
Forum: LIVE PLC Questions And Answers September 25th, 2018, 10:36 AM
Replies: 12
Views: 846
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, 09:20 AM
Replies: 8
Views: 537
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....
Showing results 1 to 25 of 500

 
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