Linear and rotary Encoder

[KinK 0]

Hi dont know much about encoders and have been asked to look into using one for an application does anyone know if it is better to use a linear or a rotary. I could use both for the application by using gearing for the rotary. I understand how they work but am just wondering what the signal is from the output of the encoder kind of confused. I guess I am going to hook it up to an omron PLC CJM1 I guess I would need a highspeed counter card. plus any brand names that you guys trust or ones i should stay away from. thanks for any help Peace

[Sleepy Wombat 27]

Depends on the application, i have used either, but the majority of the time i have used a Rotary Encoder mainly because of how they were been used...for example the speed of a conveyor, connecting the encoder to a known circumference wheel and measuring an item etc...Linear encoders have been used for a posistioning table etc...The output of the encoder will be open collector (NPN) or voltage output (PNP). Generally you will have a A,B and Z phase. The A and B phase are offset by 90 deg. This way a device such as a counter or a PLC can tell the direction. (See the Omron CPM1/2 manual for an explanation on how the encoder is wired in this instance and also how the quadrature input of the A and B phase are used to determine the direction). In regards to hooking it up to a CJ PLC you have two options, namely a high speed couter card or buy a CJ1M CPU 21/22 which have inbuilt IO of which you can connect up to 2 encoders to directly (this is the cheaper of the two options). I have used Omron, PCA and Stegman encoders.

[KinK 0]

Thanks for the answers. well I am trying to measure the stroke of a pump. it is a piston type pump and I dont really care which way it is going I just want a signal for every mm it moves. I have heard that the linear encoders dont stand up to as much abuse that is why I am asking. Peace

[Step7 0]

How about using a non-contact linear transducer as opposed to an encoder like a Temposonic transducer, here's a link http://www.davidson.com.au/products/displa.../pdf/550739.pdf Look at the hydraulic series specs (dont have to be used for hydraulic applications) They do a 0-10V version or a 0-20mA version so you could hook up to an analogue input, we've reliably used these transducers on some of our larger machines for several years with no problems (except if someone treads on one) the transducer is a non-contact type and works on a magnetic principle whereby the position of a magnet is detected along the length of the shaft and they can have a resolution of upto 0.002mm which would be more than adequate.