Old AB drives

Status
Not open for further replies.
Happy Saturday all,
I have been asked to provide in an additional pot switch in another location to modify the speed of an old A-B 1333YAB Freq. Drive for the same conveyor system. It is currently set up on a 800T-U13 pot switch in one location but they would prefer and additional one. From what I see there isn't a way to do this for I wouldn't be able to control both pots at the same time. My pitch was let me purchase a new updated drive and start over but that's not an option right now. Anyone have any ideas on how I can provide them with control of the drives speed from two different locations using pot switches?

LHarrington
 

jdsmith

Senior Member
Location
Ohio
Can you install a selector switch to select which pot to use? Not sure about the older drives, but the newer ones can be setup to have a digital input select which of two analog inputs is the active speed command. This may not work depending on how exactly your customer wants this to work.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
101106-1033 EDT

What is a pot switch? Are you simply referring to a rotary potentiometer?

Assuming the present control is a potentiometer supplied with maybe 10 V DC and thus the slider can provide an output voltage of 0 to 10 V referenced to one outside terminal, then there is no logical way to provide an adjustable voltage from two different locations by just adding a second potentiometer.

You have not described the goal of this system and related parameters.

One solution is to use two potentiometers with some switching means to select which pot has control.

A smoother operation might be to have an up-down counter connected to a digital to analog converter. The DA converter provides the output control voltage. This could be done in a small microprocessor. At each control point, and there could be many, there is a SPDT switch with spring return to center. All the switches are connected in parallel, a wired "OR" connection. One position causes the counter to increase, and the other to decrease. You could have two binary logic inputs to the processor and the counter internal to the processor.

A different but functionally equivalent method is to have an analog integrator with clamping at 0 and +10 V. The above SPDT switches are use to supply either a + or - input current to the integrator. The disadvantage of this method is that an analog integrator has some long term drift compared to a digital integrator.

.
 
Thanks I can see a switch working just fine for what they are trying to do. I tripped into this this morning currently the conveyor line is in one part of the building and the coating room is in another. I learned this morning that the coating employees need to run out of the booth to the part of building where the conveyor and panels are located to reduce or speed up the conveyor when it needs to happen. They would prefer to have the additional pot at the booth rather than running 35 yards.
I had made the suggestion to do something different and viola! tag I was it.

LHarrington
 
Gar,
I was referring to a potentiometer switch. After considering the suggestions a switch may not be practical because if the pot switches are adjusted differently at each pot switch and someone was to switch back and forth it could damage my drive. Yes I do have people how work here that would try that. After reviewing the information about this drive on the world wide wait it has limited protection from this type of scenario.

LHarrington
 
Last edited:

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
101106-1414 EDT

I still do not know what is a pot switch. Are you referring to a selector switch external to the potentiometer(s) that can switch between different potentiometers?

You need to adequately define the logic that you want this system to follow. You have now introduced the problem of a "troublemaker". How do you want to prevent this problem.

Fast switching from one input potentiometer to another probably can be handled by the ramp function in the drive, or by external filtering.

You need to start with an accurate description of the system and how it is to operate with different inputs. In other words, in your system description what action is to be taken in the case of the "troublemaker", or other abnormal conditions, as well as normal conditions.

.
 
would it be possible to have a switch in the coating area control a relay that would shunt the potentiometer with a fixed resister that would automatically slow the conveyor to a given speed and when the switch is changed the speed pot would take over
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Don't do it. On THAT drive, if you are using the external pot speed command and the Pot signal is lost, the drive accelerates to maximum speed. So if anything goes wrong in your speed selector switch circuit, the consequences are dire in my opinion.

I would either recommend they upgrade that old drive to a newer one that has dual speed control inputs, or use some sort of external device to accomplish this, i.e. one of those "smart relays" that takes the two pot inputs and a selector switch, but only puts out one analog output to the VFD.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
101106-1517 EDT

No matter what means you use for multi-point speed control you need circuitry to limit maximum speed. That could be simply a Zener diode across the speed control input with a series current limit resistor.

A 1N4733 is a nominal 5 V Zener. At room temperature using a 5 K series resistance with an actual 1N4733 the drop on the resistor was 0.19 V with 4.5 V input, 0.395 with 5.0 V in, and the Zener voltage was about 4.9 V with 10 V in.

There are ways to make a more square limiter.

.
 
Status
Not open for further replies.
Top