Reading 12 bits // encoder - Lead & Lag

[dehclau]

Hello,
I want to read a 12 bits absolute encoder which supplies 7 common bits + 5 lag bits + 5 lead bits in parallel ... yes, this gives me 17 bits to read.
Which algorithm do I have to use to get the correct position value?

Kind regards,
Cl.

[arvidb]

What's the application? Do you want to read the raw parallel signals and use them somehow? Also, what is lag and lead bits?

Arvid

[dehclau]

Application: I want to read the position of a slider. The 17 bits of the encoder is connected to a 24 digital input module according the following:
17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 <-- bit number
6 5 4 3 2 1 0 <-- COMMON 7 bits
11 10 9 8 7 <-- LAG 5 bits
11 10 9 8 7 <-- LEAD 5 bits
The combination of Common and Lag gives me a 12 bits value (gray code).
The combination of Common and Lead gives me an other 12 bits value (gray code).
a) The conversion from gray to decimal is fine.
b) There should be a logic to know which of the 2 values is the good one. That's this logic that I'm looking for.

[dehclau]

Just to complete my information, as the space characters have not been included in the previous post:
17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 <-- bit number

6 5 4 3 2 1 0 <-- COMMON 7 bits == bit 7 to bit 1
11 10 9 8 7 <-- LAG 5 bits == bit 17 to bit 13
11 10 9 8 7 <-- LEAD 5 bits == bit 12 to bit 8

[arvidb]

I still don't get the meaning of the lead and lag bits. If it's a 12 bit absolute encoder, why does it not just output 12 bits of absolute position?

I'm new to absolute encoders, as you might notice .

Arvid

[dehclau]

I think that it allows to distinguish the forward-backward direction. As for an incremental encoder ( serial coded), 2 quadrature signals allows to determine it. Only one is not enough.

[HillBilly]

The absolute encoders I have seen are like you mentioned Arvidb. In order for this one to have lead and lag you would think it would have to have a commanded postion input to calculate these figures.

Darek

[arvidb]

Yeah, if it is an absolute encoder one only has to compare the last reading with the current to determine direction... no need for "lead/lag" bits. Weird.

Anyone's got an idea what these bits are for? (Hoping for an interesting answer )

Arvid

[sbrpollock]

Can you give us details on this encoder?

Manufacturer?

Model Number?

OEM Application?

Stuff like that.

[dehclau]

If this can help:
Manufacturer: Control Techniques Dynamics Limited, UK
Contact Encoder
Type Number: 11DG216
Serial Number: 1193A0517