Digital Thermocouple Input for Micrologix 1000?

[Ron Beaufort]

it would help the forum answer your questions in MUCH greater detail if you could post the original program file ... it should have an RSS extension ... you'll have to zip it first (forum rule) ...

 

[cleansc]

Ron, attached in the ZIP is what Sensorpulse made available as "drivers" for the MSP. There are several files in their package, but I don't see a RSS file. In the technical notes (also attached), they state, "The user can import the driver into their program by standard Windows cut and paste or they can start with our driver and build their program from it".

I don't currently have a copy of the program driving our machine. Note that this machine is on that we purchased that has the Micrologix 1000 + Sensorpulse combo already on board. So the PLC, including the code for the Sensorpulses would have been programmed at the factory. I am going to try to link up to the Micrologix so that I can see/downlaod the program, but I don't yet have a cable. The local A-B distributor wanted my left leg for a cable, so I'm getting one elsewhere.

 

[cleansc]

Lancie, thanks. So, it seems we may be able to keep the PLC, add two Omega I/O modules, and modify the program.

The Omega's are $125 apiece, but I'm just worried about what the local A-B guy will charge for changing the program if I have him do it!

 

[Ron Beaufort]

I don't currently have a copy of the program driving our machine.

personally, I'd tend to worry about that situation ... if something were to happen to your processor, what would you do next? ... without having a backup copy of the program available to download, you could be looking at a substantial amount of "downtime" while waiting for someone to rewrite the program from scratch ...

I am going to try to link up to the Micrologix so that I can see/downlaod the program,

be careful ... with an Allen-Bradley system, the operation that you're talking about is defined as an UP-load ... specifically, you would UP-load the program FROM the PLC processor TO the computer in order to "see" it ...

The local A-B distributor wanted my left leg for a cable, so I'm getting one elsewhere.

the link below is one good source for a cable – and the guy who runs the company would be willing and able to explain how to set up the connection ...

http://www.ind-concepts.com/

do you already have a copy of RSLogix500 – and a copy of RSLinx? – installed? ...

good luck with your project ...

 

[Lancie1]

There are several files in their package, but I don't see a RSS file.

There is one called "MSP_I.RSS", plus the same program in the older DOS-type PLC program files. The RSS file has the SensorPulse file saved as an STI Interrupt file in LAd 5. It reads Input I:0.0/0, computes the analog value, and appears to save the result at memory location N7:9. This program uses bits or words in memory words N7:0 to N7:9.

The Omega's are $125 apiece, but I'm just worried about what the local A-B guy will charge for changing the program if I have him do it!

Perhaps Omega has a "driver" program similar to the SensorPulse program that can be loaded on your MircroLogix. If minor changes are needed in such a canned program, we can help you with those. Because you have two thermocouple inputs, someone at one time had to duplicate the routine and change addresses for the second temperature input. That will not be too difficult. There was another program listed in the DOC file called MSP_I_M.RSS that is for multiple inputs, so that one might have been the one actually loaded to your MicroLogix.

 

[Lancie1]

Here is a PDF copy of the MSP_I.RSS Lad 5 file (the only file with any rung logic).

 

[cleansc]

personally, I'd tend to worry about that situation ... if something were to happen to your processor, what would you do next? ... without having a backup copy of the program available to download, you could be looking at a substantial amount of "downtime" while waiting for someone to rewrite the program from scratch ...

Yes, I completely agree. The company that produced these machines has been out of business for years, so we definitely need the control logic. It's not a highly complicated machine, but nonetheless...

"be careful ... with an Allen-Bradley system, the operation that you're talking about is defined as an UP-load ... specifically, you would UP-load the program FROM the PLC processor TO the computer in order to "see" it ... "

Thanks for the clarification; wouldn't want to overwrite it!

"the link below is one good source for a cable – and the guy who runs the company would be willing and able to explain how to set up the connection ...

http://www.ind-concepts.com/

do you already have a copy of RSLogix500 – and a copy of RSLinx? – installed? ... "

"I have a copy of the RSLogix Micro Starter Lite / RSLinx Classic Lite that I was hoping to at least see and document the program once I got the right cable. Can these versions also be used for light programming? "

Thanks for the info.

 

[cleansc]

Here is a PDF copy of the MSP_I.RSS Lad 5 file (the only file with any rung logic).

Awesome. Thanks Lancie.

 

[Lancie1]

Thanks. I have a quick question: Does your SensorPulse module accept 2 thermocouples, or just 1? (In your posted picture, I see only 1, but I was just making sure instead of AssUMeing.

The reason I ask is that the program you have is only set up for using one count input and then uses 1 more input at I:0.0/9 called MSP Hardware Input. I assume this is a bit that tells the PLC program that the SensorPulse module is installed and active. It seems that for two thermocouple inputs, you would need 2 additional inputs (assuming that your thermocouple module only accepts one T/C).

 

[cleansc]

Thanks. I have a quick question: Does your SensorPulse module accept 2 thermocouples, or just 1? (In your posted picture, I see only 1, but I was just making sure instead of AssUMeing.

The reason I ask is that the program you have is only set up for using one count input and then uses 1 more input at I:0.0/9 called MSP Hardware Input. I assume this is a bit that tells the PLC program that the SensorPulse module is installed and active. It seems that for two thermocouple inputs, you would need 2 additional inputs (assuming that your thermocouple module only accepts one T/C).

That's right; each module accepts only one TC input. We have two modules, one for each TC, inputting to I/0 and I/1. Note that the file I uploaded is the "canned" code provided by Sensorpulse and not the code actually running in our machine. I expect to find in our machine when I can see the code is that there are two sets of code, one for each module.

 

[Tom Jenkins]

I'm going by memory here, and I didn't decipher the code "MSP_I.RSS Lad 5 file". however, I believe the SensorPulse doesn't need a high speed counter input because it sets up a pattern of bits that come in slow enough for a regular input to catch them. On the other hand the Omega and Calex unit have a signal that goes up to 2 kHz, which is faster than most regular inputs can handle. I believe you must have a high speed counter input for each Omega unit.

 

[cleansc]

I'm going by memory here, and I didn't decipher the code "MSP_I.RSS Lad 5 file". however, I believe the SensorPulse doesn't need a high speed counter input because it sets up a pattern of bits that come in slow enough for a regular input to catch them. On the other hand the Omega and Calex unit have a signal that goes up to 2 kHz, which is faster than most regular inputs can handle. I believe you must have a high speed counter input for each Omega unit.

Interesting you mention that because I didn't see the HSC referenced in their code and in their patents and technical information, they refer to the identification and pulse signals as being in multiples of the scan time, which I assume means that they're giving the controller ample time to read the signal accurately.

And I had just noticed that Omega has two different classes of I/O's in this category: one for high-speed (to 5100 Hz) and one for low speed (to 1100 Hz). (http://www.omega.com/DAS/pdf/DRP-8500.pdf)

In this application, we can live with fairly low resolution (+/- a few degrees), so would there be any compelling reason to use the higher speed input?

Thanks

 

[DamianInRochester]

I think that was the key to SensorPulse's technique. You could use a standard input on a plc with a relatively long scan and still transmit the value. They cheat a bit by not updating the entire value all the time.

 

[Tom Jenkins]

In this application, we can live with fairly low resolution (+/- a few degrees), so would there be any compelling reason to use the higher speed input?

Yes, but it has nothing to do with resolution. Even at the lower range, 1.1 kHz, a standard input may not pick up the pulses. 1/1100 = 0.909 ms. That means that if your PLC scan time is longer than 1 milisecond you will miss some pulses. That would be true even if the input response time were good enough to pick up a pulse less than 1 milisecond long, which is doubtful.

High speed counter inputs have fast response hardware and their own dedicated processor to pick up this kind of pulse. A regular PLC input just won't cut it.

 

[Lancie1]

In the SensorPulse MicroLogix 1000 program, they did use the IIM instruction to read Input Word I:0 (all 16 bits, then bit I:0.0/9 is pulled out and saved to N7:5/0 "MSP Input Contact"). That should make the time between pulses much shorter than a normal scan. Probably the limitation would be the speed that the input can switch from ON to OFF. Also, the Thermocouple input routine is inside a STI (Selectable Timed Interrupt). The STI is set to interrupt the normal scan every 10 mseconds (the minimum allowed setting. It seems that this would be the bottleneck to determine how fast the T/C digital ON/OFF input has to change.

IIM [Immediate Input with Mask]
Rockwell Software
This output instruction allows you to update data prior to the normal input scan. When the IIM instruction is enabled, the program scan is interrupted. Data from a specified I/O slot is transferred through a mask to the input data file. This makes the data available to instructions following the IIM instruction in the ladder program.

Selectable Timed Interrupts [STI]
Use this function to interrupt the scan of the main program file automatically, on a periodic basis, in order to scan a specified subroutine file. Note that this differs from a standard subroutine interrupt because you can specify the time interval when your STI routine will execute, by placing a value in Status Register Address S:30.
Rockwell Software