(Very) Basic Powerflex 753 question

SamW

Member
Join Date
May 2016
Location
Ludlow
Posts
9
Or more accurately 2 questions, 1 very basic, the 2nd potentially a little more complicated.

Background: We're using a 753 drive to control a single motor. This motor runs at one of 2 speeds, depending on the level in a hopper. At present the low speed setting is set by the Reference Speed on the inverter, the high speed is set using Preset 4 (parameter 574), hopper level is read using a laser, giving an analogue signal.

1) Can anyone give me a 2 line explanation of what the reference speed is intended to be used for.

2) How would you set up the control for the situation we've described above?

Look forward to hearing your answers
 
1. The 753 can have several speed References. The reference used is determined through the VFD internal logic. There may be a "preset reference" as would be Param#574, but there may also be an analog reference driven by your level transmitter. There are several different ways to change which value(reference) is being used, and that becomes the "Commanded SpdRef", and then if the VFD is commanded to run the "Commanded SpdRef" may become the "Output Frequency". In the 753 programming manual is a flow chart that illustrates how the 753 decides what reference it will use.

2. The 753 has built in DeviceLogix. My suggestion would be to use the level transmitter to drive your reference speed, until it reaches a certain value. At that point it could change the reference speed to you preset speed. All this is done through "Connected Components Workbench" software, which is a free download through the AB website. Programming for DeviceLogix may be more difficult than what you'd like, though. If your level transmitter has a FormC contact that is programmable, you could use that to actually cause the 753 to switch references. I'm not really sure, since I do not know your equipment.
 
...

1) Can anyone give me a 2 line explanation of what the reference speed is intended to be used for.
It is what you use to determine what you want the motor speed to be. In this case, your 4-20mA signal or preset speed.

2) How would you set up the control for the situation we've described above?
I would first decide ALL of the command and control conditions by interviewing all stakeholders.

For example, you mention SOME of the situational issues, but not all of them. How / what decides the change from the 4-20mA signal or the fixed speed? Why? Who is going to make that decision and how? What happens if something doesn't work right? What do you want it to do if there is an overload / underload / power loss / control signal loss / emergency stop / maintenance service stop / etc. etc. etc.
 
my guess
The reference speed is the minimum speed the hopper should fill regardless of the analogue signal, the higher speeds are controlled by the analogue signal.

Steve
 
Thanks for the replies, giving me some extra avenues to start looking down.

Bit more info on how we're working. The 'Ref' speed is set via the HIM and it's a constant, typically 21Hz. To set it we push the button with Ref written above it on the main screen.

Preset 4 is typically set 3Hz higher

All the analogue signal is used for is to tell the VFD when to swap from one to another e.g. below 50% full, run at Ref, above 50% run at Preset 4.

This generally works OK, but I do feel that we could use the analogue signal to produce a variable speed command, leading to more consistent hopper emptying.
 

Similar Topics

Im looking to hook up a 3 wire PNP photocell to an Allen Bradley 1746IV 16 module. Ive watched videos about hooking up DC sensors, but they show...
Replies
3
Views
2,871
I finally have my test/learning bed set up at home. I understand logic and programming, there are some holes in my basic electronics knowledge...
Replies
6
Views
3,344
Hello, I have an application where I will need to use the Serial port in a L55 CPU, and I can go about it in two ways, but both require me to...
Replies
2
Views
1,473
Hello, Forgive the basic question, but I've been having a hard time finding a clear answer to this online or otherwise. I'd really appreciate any...
Replies
10
Views
2,179
I will apologize in advance for this question. In a PLC scan I understand the inputs are read, then the PLC carries out a scan out the logic and...
Replies
11
Views
4,098
Back
Top Bottom