TOFR - non-retentive timer

einnh

Lifetime Supporting Member
Join Date
Mar 2014
Location
New England
Posts
275
I have a question about the TOFR instruction, a non-retentive timer that accumulates when the input bit goes low.

For me this is in Rockwell's Studio 5000 v26.

The documentation shows that the .dn bit goes low when the timer is done. This is opposite of what happens with the TONR instruction. Is this accurate? I thought .DN was supposed to indicate when the timer was done. So shouldn't it go high?

2015-06-26 11_02_40-Logix Designer Online Help.png
 
"TOF" means Timer Off Delay, so it works sort of opposite or the inverse of the TON (Timer On Delay). TOF means DN will be ON when the timer receives a true rung condition, and only time and the DN go OFF when the rung goes from true to false.

I think the "R" at the end of both instructions means Retentive (the timer will hold its time ACCumulator value until reset). Are you sure that TOFR is a non-retentive timer?
 
The TOFR is a non retentive timer for FBD and structured text only.
In ladder it is the same as a TOF plus a RES.

The time interval is from the EN going low to the DN going low.
 
Thank you for the quick replies.

I'll stick with TONR and 'not' statements as .DN being true when not done and false when done hurts my head.
 
I think it helps to think of the DN bit following the state of the input condition, just delayed. For example, using a TON with one rung condition - imagine an XIC contact - the DN bit is unconditionally false when the rung is false*. When the rung goes true, some time later the DN bit will go true. With a TOF when the rung is true the DN bit is unconditionally true*. When the rung goes false, some time later the DN bit goes false.

Given that, the TOF is a strange critter to get your head around.

YMMV

* assuming the rung is being scanned
 

Similar Topics

TRIGGER.PRESET := 1000; TRIGGER.TIMERENABLE := (TAG1=TAG2); TOFR(TRIGGER); ANOTHER_TAG := TRIGGER.DN I want to compare two tags and...
Replies
4
Views
1,641
if we need to take back up of Siemens CPU(s7300 /s7400) with non siemens slave profibus nodes without their gsd files and when we restore it in...
Replies
0
Views
67
Hi all, I have installed a SICK AFM60A-S4IB018x12 encoder to Allen-Bradley CompactLogix PLC and configured its parameters via AOI provided by...
Replies
0
Views
82
Hi, I'm trying to understand a couple of things with a feedback signals that are used in a SRP/CS that I'm working with. Quick disclaimer: I'm...
Replies
2
Views
492
Hello, has anyone ever been caught in this situation? You have redundant CPUs, fieldbus is PROFINET, there are some devices which don't have the...
Replies
0
Views
501
Back
Top Bottom