dan_did_it

What 1756 Input module will work with a 845D Gray Code Encoder

9 posts in this topic

Hello, 

I am migrating a PLC-5 to Control Logix.   Due to location etc, we need to keep the existing 845D-SHHZ25AGCW4 Encoders.  (256 counts, single turn 24vdc NPN open Collector.)

I tried to use a 1756-Ib16IF, but I toasted my spare encoder.  (Have to get another one).

My question is has anyone ever done this since the 1771-DL is not made in CLX form factor.   Also, what Module did you use if you did try this and if you have a wiring diagram, 

would be great!  (I cannot afford another fried encoder)

Thanks!

Dan

Edited by dan_did_it

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I can't give you direct advice because I have not specifically done this migration.

The 1771-DL is electrically pretty simple, but has a wider input voltage range than most DC input modules (from 10 to 27 volts DC).    You can see the simple sinking inputs in the user manual for the module:

https://literature.rockwellautomation.com/idc/groups/literature/documents/td/1771-td029_-en-p.pdf

The 1756-IB16IF should have been ideal for this application.    It has fast inputs (the -DL had 1 ms filtering and the -IB16IF has 14 us) and isolated DC inputs that accept 10-30 V DC as either sinking or sourcing circuits.

The 1771-DL also had a triac zero speed switch on the bottom two terminals that was intended to be used with 120VAC motor control circuits.   You definitely don't want to hook up any of the conductors that might have been involved in that to your 1756 module.

The 1771-DL used sinking inputs:  you connected +24V DC to the module, and the encoder drew the input signals to DC Common.    The user manual says:

Quote

The encoder driving circuit sinks 15 mA at 24 VDC or 6 mA at 12 VDC per Gray code input. Multiply this by eight for each encoder powered by this supply

So the encoder should be sinking 15 x 8 = 120 mA or so.

How did you hook up the 1756-IB16IF ?    I can't imagine a way to connect these devices that would damage one of them unless you put greater than 30V DC on the circuit somehow.

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I believe I toasted it when I accidentally swapped polarity of the 24vdc to the encoder.

(I fried the encoder, not the module)

i am still apprehensive that possibly something else damaged the encoder?

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Thanks very much for posting that photo !    It brings back memories of my childhood poring over the TTL Cookbook.

The chip looks like an SN7407 "hex buffer", which interfaces "high" voltage to low voltage TTL and CMOS circuits.   

It looks like Pins 2 and 3 or 3 and 4 blew up, which would be Input 2 or Input 3.    I can't say why those would be damaged by a 24V supply power inversion to the encoder.   That should have been prevented by one of those big honking diodes.

All I can recommend is carefully applying 24V to the encoder, only after terminating all the DC outputs to the Input module so they can't short to ground or touch anything else.

 

 

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Thanks Ken.

inwill post a drawing of how I think it’s sposed to wire to the 1756-IB16IF tomorrow.

let me know if you think there is something wrong with my thought process.

THANKS!

Dan

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I have attached the copy from the Rockwell manual of the 1756-IB16IF module, I also attached a copy of the way I wired it to the 845D Gray code Encoder (NPN Open Collector).

Ken, see if you think I goofed up.

Thanks!

Dan

I756-IB16IF.png

I756-IB16IF_ENC_WIRING.png

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Hi

Dan, your wiring is correct assuming that the module's terminal 34 be connected to both the encoder pin T and the negative of your 24Vdc supply

Bye

 

PS Excuse me for my intruding

Edited by chantecler
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Hi Chantecler!

you are definately not intruding!  I appreciate your comment.   BTW I am a big fan of U of M !  I grew up in Michigan not far from there  :)

Yes, terminal 34 will be connected to encoder pin T and the negative of the 24vdc power supply.

Dan

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