24 Bit Words???

jameskelly.ie · Apr 9, 2007

hey guys i've only been using plc's a few months for my final yr project in mech eng.
i'm using an omrom cpm2a and mad11 expansion unit to implement and antisway controller on a gantry crane!!

anyhoooo my q is this
the omron has a 16 bit word which is fine except when using signed binary i'm limited to +/- 32000 ish
which unfortunatly aint good enough to do the job perfectly

the plc dosnt support floating point numbers.. so
what i'm wondering is if there is a plc out there (any manufacturer)
that uses 24bit words (5 hexadecimal numbers) or do all plc's use 16 bit words??? thanks for any info!

Tharon · Apr 9, 2007

Some use 32 bits, I think Allen-Bradley calls them Double Integers, I dunno what the other brands call their similar datatypes.

I've not been exposed to many brands (Automation Direct, Allen Bradley, and Siemens are pretty much all I've seen). But 24 bits doesn't seem to be a standard at all (very odd number I believe).

jameskelly.ie · Apr 9, 2007

thanks tharon, yes 24 is an odd number i suppose it makes more sence to jump to 32, just picked 24 because of 24bit audio i guess!!

CroCop · Apr 9, 2007

jameskelly.ie said:
hey guys i've only been using plc's a few months for my final yr project in mech eng.
i'm using an omrom cpm2a and mad11 expansion unit to implement and antisway controller on a gantry crane!!

anyhoooo my q is this
the omron has a 16 bit word which is fine except when using signed binary i'm limited to +/- 32000 ish
which unfortunatly aint good enough to do the job perfectly

the plc dosnt support floating point numbers.. so
what i'm wondering is if there is a plc out there (any manufacturer)
that uses 24bit words (5 hexadecimal numbers) or do all plc's use 16 bit words??? thanks for any info!

I've got a crane that does antisway that uses all calculations in INT, 16 bit. The pendelum length is CM, the speed ref is +-10000, FWIW.

rajy2r · Apr 9, 2007

I dont think u can have 24 bit words. Dont they just go in powers of 2.

1..2..4..8..16..32...................

TimothyMoulder · Apr 9, 2007

You can, and do. It's more common in motion control than PLCs, Trio is one example. Actually, kind of a pain in the butt, I'd rather have 32-bit, but it was their call when they designed the architecture. I'll forgive them - they make good motion controllers.

Aside from that, most PLCs have something for 32bit these days. Double-Word, Memory Long (ML), Long Integers, etc. Depends on the brand.

TM

BobB · Apr 9, 2007

You are using a PLC with fairly old technology and low resolution analogues. Suggest you go up to the CP1 which will use the same expansion I/O but has 64 bit floating point and other maths, and 32 bit of course.

Time is leaving the older shoeboxes behind now.

24 Bit Words???

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