Grasso - 9 cylinder Compressor - Ammonia

Hello all you experts!

Please bear with me..... this may be a long one!

And this will probably sound VERY 'novice'.... because it is!!

I am a software / "machine tool controls engineer" and was recently called to replace a failed Omron PLC controller sitting in a refrigeration compressor control panel.

The customer didn't have schematics of the control panel / system, only hand drawn notes on what appears to be a PLC addition / upgrade to this panel.

Also, there's no record of the program that WAS held in the failed PLC, no software back-up or a printed program.

We have failed to contact anyone who may know the contents of the lost programme. So this is a plea for help / comments / direction / contacts / advice / drawings!? etc.

It was obvious to me on my first visit to the customer, that this was a problem needing specialist refrigeration knowledge, therefore I requested that they contact a refrigeration specialist to assist me with the 'logic' of the process so that I could convert this into PLC 'code' for the replacement controller.

My customer did this, and in the interim period (before procuring a new PLC controller) he advised a 'hardwired' fix to get them back into production (Ice Cream Factory) This involved directly connecting the 'loading stage' solenoid valves to the pressure switches monitoring refrigerant pressure.

I seem to be 'rambling on a bit' so let me first tell you what was originally connected to the PLC controller........

INPUTS....
1 - 'Increase' from a Manometer
2 - 'Decrease' ---------"-----------
3 - 'Relay R2 - Compressor Safety Interlocks all OK'
4 - 'PS1' (Refrigerant Pressures' ?)
5 - 'PS2'
6 - 'PS3'

(The bit in-between is missing! ie. the prog!)

OUTPUTS.....
1 - 'Relay R1 - Start Compressor Motor'
2 - 'SV1 Load Stage 1 Solenoid'
3 - 'SV2 Load Stage 2 Solenoid'
4 - 'SV3 Load Stage 3 Solenoid'
5 - 'SV4 Load Stage 4 Solenoid'

The 'hardwired' temporary mod was to connect the system such that as soon as the motor changed from 'star' to 'delta' SV1 would be energised.

Then wired so that PS1 would directly energise SV2 (Load 2)
PS2 would call SV3 and
PS3 would call SV4.

The system then ran ok for a number of hours, until the temperature got quite low (-0.5bar on manometer) then soon after this the ice that had formed on the compressor suction started to thaw, and the customer informed me that temperature was 'rising' at the 'business end' on the production line!
(sorry for my incomplete specialist jargon!)

The obvious ommission from this 'hardwired' temporary fix is the manometer connections, so while we are trying to find someone to visit site to advise us, can you tell me what effect the manometer inputs should have on the 'loading valves' ? Bearing in mind that the PLC only had control over the Compressor Motor starting and the 4 loading solenoid valves.......

We are having trouble getting the 'specialist' back (too busy elswhere) so in the mean-time, is there anyone out there that may be familiar with this type of PLC modification, a PLC that only has influence over the Loading Valves based on the status of the 3 pressure Switches and the 'increase' and 'decrease' signals from the Manometer?

BTW, please don't SHOUT at me, I realise I know very little about refrigeration theory...... but if you want me to play a tune on a PLC controller, just hum it for me !!

I look forward to your comments.
Regards, Richard.

rlmts@controlit.fsbusiness.co.uk

hi richard
the program would seem ok in that a increase from manometer starts compressor, delta loads sv1 then time delays or increase in manometer energise sv2, sv3, sv4
but to be loosing duty at -0.5 bar would suggest a problem with process or the plant not controls. because at 0bar gauge NH3 evaporates at about -32 or is it -33 C anyway -0.5bar is way too cold for ice cream find a good fridge company to work alongside you for a day and bottom out the problem.
PS its not richmond ice cream is it
regards calders

Calders it's not Richmond Frozen confectionary they don't have a plant in Wales and they have a contractor working along side there own engineers
York Refrigeration

Hi rlmts:)
the pressure switches are replacing the contact manometer, but the manometer has a finer differential (difference between the cutout and the cut in) so control will not be as fine, hence the high temps before the compressor cuts in, or the low pressures before the compressor cuts out.
There is off the shelf controller for this type of application, ADAPKOOL and even eliwell, but if you want to use a plc you need to fit a pressure transducer and an analogue channel (input) to the plc and an appropiate power suply to the transducer. Then you need to determine the initial start delay on rise of pressure, the time between stages, the delay before a stepdown is called for once the pressure drops and the delay between stages on the way down, the load % to run at for minimum and the delay before stop at minimum. You would also need the cut in and out pressures and a little conversion to determine what voltage/ma this set points are.
What is the application, storage or making ice cream:confused:
If you post back some more info on the plant we could possibly give you some pressures.
Kind Regards. Andy:)
Ps you could advise your customer that there is other companies other than York who maybe willing to help such as Grenco or Star.

Hi Marc:)
cost is relative, people look at an hourly rate and say I can't afford that. But if you get the right technician on site, the job will take him a lot less time than somebody at half the cost who is charging what he is worth.
You know the old saying "you get what you pay for"
Regards. Andy:D

Mark having read quite alot of your posts you appear to have a thing about York or am I imagining this ? Have you been turned down for a job in the Past ?

Hi torque:)
I can think of another company he is not too keen on:D the one I work for:D :D
But Marc still converses with me no bother;)
Regards. Andy:)

Mark a very intresting story , without a doubt you sound like a very very very intelligent guy who knows his onions but you are implying that everyone who works for York are thick as **** and crap at there jobs.
It's not healthy to carry things like that around with you let it go and move on.
Evey success working for yourself because you've had the balls to do it.

Sorry about that Rlmts just suggest to your customer he should retrofit a Unisab two to his 9 cylinder Grasso

Hi;

This post have been very interesting for me. I´m writting for two things:

1. Is there any web site or papers for learning refrigeration logic, i mean: the most common inputs - outputs?

2. On the other hand, i´m a sales engineer working for Grenco in Spain and my main competitor is York. My question:
Here in Spain York is very aggresive with prices, Is the same outside Spain?

Best regards

Here in Canada the lower price is mycom with others close behind it will make a difference if you are a "dealer" this has different meanings for different manufacturers. I work in sales here.
wesmax

Hello Guys just one query on plc logic for fridge systems having safety switches as inputs to the controller I have always thought this was a no no I have always believed these have to be hard wired so they can not be forced through control logic?

Regards
Dave G

is this Thayers

Quote:

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Originally Posted by dwrefrigeration

is this Thayers

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I dont understand the comment
wesmax

Was This problem at Thayers Ice Cream

Quote:

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Originally Posted by dwrefrigeration

Was This problem at Thayers Ice Cream

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yes what is the meaning of this

Hi All,

Sorry for not getting back onto this forum to acknowledge the earlier posts (mind you, I think I started to loose a bit of interest when my post thread was being used to discuss the vitues of various service companies ;) )

But, that's no excuse!! I have mainly been busy elswhere in my area of expertise (Machine Tools)

Yes it was Thayers, but it was back in July 2003.

They have since moved from Cardiff up to a new site and factory in Cwmbran.
They now have their own controls engineer/electrician/technician, and I haven't been back there for a year or two now.

Regards Richard.

Once again, sorry for not acknowledging earlier.

Richard
I was the refrigeration engineer who met you on site to hard wire the panel.Thats how I knew it was Thayers
David Whitcombe

Quote:

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Originally Posted by torque

Calders it's not Richmond Frozen confectionary they don't have a plant in Wales and they have a contractor working along side there own engineers
York Refrigeration

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Andy, Why was York brought into this discussion?
Marc, you may have grievance with a local York office but I would ask you don't tar every branch with the same brush.........you may show yourself up (no change there then):)

MMMMMMMMMM lot of things ring bells here.....

I used to work for a certain little industrial compressor manufacturer from denmark.... Then a certain afore mentioned American company decided to buy them out.... Stuck it with them for a few years and because we actually retained our identity and individuality it wasnt to bad.
But the bible EBIT soon became to much to bear and it was time to go

Quote:

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Originally Posted by Dave Goodings

Hello Guys just one query on plc logic for fridge systems having safety switches as inputs to the controller I have always thought this was a no no I have always believed these have to be hard wired so they can not be forced through control logic?

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It should be a no-no for HP, LP and Oil safety switches, plus any interstage protection. The same for temperature protection stats. This is if the compressor can be run on hand, as running in this mode may by-pass normal control routines in the PLC. It is not unknown for a PLC control to crash through supply voltage faults for example. Someone then comes along to run a machine on hand "until someone technical gets here".

However, if control routines are inserted to ensure ANY fault condition met ensures total shutdown then maybe OK, but if it was ammonia, I'd go for belt and braces. To be honest, I've never come across a plant without hard-wired safety's.

Steve

Quote:

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To be honest, I've never come across a plant without hard-wired safety's.

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We've recently taken over maintenance of 2 Dunham Bush chillers (240kw each) and all safety measures were through the software :eek: (we've put in hard wired LP and frost stat safety switches so far - looking at other options at the moment)

Hi Richard,

Have you resolved the loading and un-loading of your Grasso compressor? If not is the compressor model a RC 63 11 or RC 63 12?

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