Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Sensor Question, Plz Help!!!!

Status
Not open for further replies.

linkyta

Newbie level 5
Joined
Sep 2, 2005
Messages
9
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
Mexico
Activity points
1,384
Hello Guys, im a beginner here and for a control project I need to design a position control for an elevator. It has to be done using analog devices and the first question is: how do I measure position??? I have some ideas, but since I have no previous experience I really really need suggestions.

(by the way, I cant use a potentiometer):cry:

My ideas are:

•Place a magnet at the bottom of the elevator and measure the magnetic field (do you know a cheap sensor????)
•some kind of ultrasonic sensor
•measure light variation in someway, but i think it's kinda hard 2 asure the quantity of light in the model

Id really appreciate your helping hand here, since Im running out of ideas, it doesnt have to be an ellaborated system, in fact, the teacher wants it to be ingenious

thanks a lot
 

There are other sensors or transducers for measuring or indicating position, like linear variable differential transformer (LVDT), IR sensor, ultrasonic ranger that measures distance, magnetic position sensors and proximity sensors like Hall effect sensors (based on magnetic field). but since you have to deal with analog circuits exclusively, I suggest the Hall effect sensor for your application. You can find such sensor at Honeywell.

You can find additional information on the Hall effect sensors at:

**broken link removed**
**broken link removed**
 

    linkyta

    Points: 2
    Helpful Answer Positive Rating
I assume this is just a model that you are making?. I cannot think that hall effect devices will be much use in this application apart from as a switch. Possibly ultrasonics may be your best option. An alternative would be a rotary position encoder wrapped round with a string and a weight on the other end. The normal way to do this of course would be to have switches on each side of of every floor, one of these before the floor to tell the lift to start slowing down, and the other switch to stop it at the required level. Actually lift control is quite a complicated subject, and not as easy as it first appears. Good luck!
 

    linkyta

    Points: 2
    Helpful Answer Positive Rating
Thanx a lot for the hints, and yes, it's just a model of about 0.50m ( i dont know that in inches, maybe 125? :D) and I've thought about a LVDT, but the comercial ones are way too expensive and only have a few inches range, do you think it's possible to actually build one or something similar for my model??

the good thing is that i dont need to put actual weight in it, and the position has to be measured continiously (u dont need to be telling which floor you are in)

and thank u all for your help!!!
 

Yes LVDTs are usually short range but you can get long ones, as you say they are expensive. I still think a rotary encoder of some sort would be the best solution. What you need is a pully on top of the shaft with a couple of turns of low stretch wire etc round it. One other end can go to a weight that hangs down at the side of the cage and the other of course to the top of the lift car. Rather than the weight if you could devise some sort of spring return on the pully, this would be ok as well. The idea is to keep the cord under slight tension so it does not sag when the car is rising. If you then have a shaft the comes off this pully, you can drive a rotary encoder of some sort, possibly even a multiturn pot if not too stiff. Hope this helps.
 

Hello,

If you are talking about a model of an elevator, and you are limited to a analog sensor, I think that the easiest solution is to use potentiometer in the axis of the upper pulley.
Just remember to adjust your control system as overdamped. Your "toy passagers" would not positively apreciate an elevator with overshoot in its temporal response.
Best regards.
 

Thank u all for your advise, it's been really helpful lads since I really had no idea how to do it (i have a slight idea now :p)
 

In the practice, proximity sensor is used for detecting position of elevator. You can search more literatures with key word proximity
 

Most elevators use magnetic reed switches or inductive proximity sensors to determine position. The exact position is not important between the floors. It is only important when you are near a floor. Noramaly a slow position and a stop position are all that are required for a floor.
 

Just a further thought,

If you can use a stepper moter to operate the lift. You could count the number of pulses and direction changes
in the mcu program that I presume you would use to drive the motor. This of course would tell you where the lift was at any time. You would probably need limit switches at the to and bottom of car travel so that you could set you initial point to count from.
 

Oh yeah GrandAlf, I thought about counting the number of pulses and such, but I cant use a mcu :( but thanx for the interest!

Another question though: I've been searching for hall effect sensors and in the specs some say

Operational type: current sink
Operational type: latch

what's the difference??

(im sorry if these questions are somewhat silly, but Im a begginer here LOL) thanx again
 

Current sink = low output (ground) when energised, i.e a relay connected between output and + supply. Latch comes on when sensor activated and stays on even when source of trigger is removed, usually power off to reset. Its not going to make it easy without an mcu. Reaaly your options are an analogue sensor system, or as stated before, limit switches around each floor and a 2 speed motor with possibly a relay interlock system. I really do not think that you can use hall effect sensors to accurately measure distance, but good luck anyway.
 

    linkyta

    Points: 2
    Helpful Answer Positive Rating
Thanx alot for the definitions, they're really helpful and yeah im considering that the hall effect sensor isnt the propper way to do this.:|
 

hi
there are two type of position sensor
1-absolute position sensor
2-relative position sensor
linear petansometer is an absolute sensor
optical encoder is relative sensor

phillips(tm) co. have one absolute type . In a fixed
steel rod the fundamental ( resonance) ferq. depended to length of rod .
a moving magnet can change fixe point (therefor length ) of it.
by measeruring the ferq. of rod by a piso sensor
position is measurred.
 

Hey smxx thanx 4 the hints, I've been in the phillips website but I cant find the sensor u tell me. Do have any part number o some keyword to search for it? thank u :)
 

dear linkyta
I use 4 second hand of this sensor for balancing a
Hydrolic press unit last year.
plz wait ,i must ask my frindes in that co.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top