Micrologix 1500 counter help

[Lancie1]

When I am told I should use things like LIM comparison or/and PID block I really don’t know what these are.

The good news is that you live in a country with free speech and free knowledge. You are allowed to look up the LIM instruction and learn about it, without needing to get permission from anyone! I just don't understand this pattern of young guys thinking that they have to have permission to learn new things! Is it the result of the modern regimented education system? I started school in a one-room schoolhouse, 8 grades with one teacher. I learned by listening to the older kids. Whatever you could do, that is the grade that you were in for that subject. By the 3rd grade I was doing reading, science, and history with the 8th graders while still 3rd for writing, health, and spelling. This school was controlled by the local parents. Now schools are controlled by stuffed shirts in D.C. who know or care nothing about local conditions.

You said that you had a 1769-OF2 Analog Output Module, but if you do, its address cannot be O:0.1. It would be something like O:1.0 or O:2.0 depending on which expansion slot your analog module is installed.

Because you do not have any feedback from your drive (Process Variable), then a PID is not really the best solution. Instead like Okie said, simply use a math computation (SCP for your ML1500) to scale a calculated RPM to your drive Speed Setpoint Input (the count range of your 0-10 volt output, which is 0 to 10000 for the "Engineering" format according to the 1769-OF2 manual. Only about 5 or 6 rungs are needed. Probably some of these with the ONS One-Shots could be combined, but from past experience some MicroLogix PLCs are picky about having more than one instruction on the right side of the ONS.

Before you ask, here is how the SCP instruction works, from the RSLogix Help file, in 6 easy lessons.

SCP [Scale with Parameters]
Rockwell Software
Input - Enter a value to be scaled. This can be a word address or an address of floating point data elements.

Input Min - Enter a minimum value for the input (low end of range). This value can be a word address, a long (double-word) address, an integer constant, floating point data element, or a floating point constant.

Input Max - Enter a maximum value for the input (high end of range). This value can be a word address, a long (double-word) address, an integer constant, floating point data element, or a floating point constant.

Scaled Min - Enter a minimum scaling value representing the low end of the range to which you want to scale the input. The scaling relationship is linear. The value can be a word address, a long (double-word) address, an integer constant, floating point data element, or a floating point constant.

Scaled Max - Enter a maximum scaling value representing the high end of the range to which you want to scale the input. The scaling relationship is linear. The value can be a word address, a long (double-word) address, an integer constant, floating point data element, or a floating point constant.

Output - Enter an address for the scaled value that is returned after the instruction is executed. This value can be a word address, a long (double-word) address or an address of floating point data elements. If any floating-point file types or floating-point constants are encountered in the above parameters, then the entire instruction is treated as floating point, and all immediate integer data values are converted to immediate floating-point data values.