Two Unisab II Problems

[Tung]

Gentlemen,
I have two Sab202 compressor units that use with Unisab II, both of them have problems that cause the units in malfunctional condition,
1. Sab 202 SM with Unisab II, Version 2.04, the compressor will automatically start in manual mode, and can not be stopped by pressing O, what could be the problem? Software or the relay?

2. Sab 202 SF with Unisab II, Version 2.01,
at first, the compressor shutdowned for capacity error, when it stopped, the SV% reading was 35% and the compressor couldn't be reset and restarted, some technician has readjusted the angle transmitter but didn't work,
when I was on call to the job site, I sent 4-20mA signsls directly to the controller(terminal 30/31), the indications on the display was correctly corresponding to the signal(4mA-0%, 20mA-100%) I sent, then I took off the transmitter to measure the mA by turning the transmitter shaft, the parameters on my multimeter was swinging, so I suspected the transmitter is defective;
Today I had the defective transmitter replaced by a new one, before installing, I ajusted the Zero and Span screws in corresponding to Capacity Slide 0% and 100% position I had marked last time(by turning the shaft),
when compressor started, the 0% indication on the display suddently dropped to -23%, and then with the compressor started loading, the indication swinged up and down, and finally stopped at 78% with the compressor fully loaded, I manually stopped the compressor, the indication was 0% when fully unloaded, I had repeated the start-and-stop procedure for several times, and every time I got the same result,
I measured the 24VDC supply on terminals 29/31, it read only 20.5 VDC and the reading also swings,
now I am just totally confused, what could be the causes for this abnormal condition, defective board? or just improper adjustment?

Any advice will be much appreciated.

[ping]

in the second case try to configurate it as sab163.

[Tung]

Angular Position Transmitter.

[Tung]

Ping,
What you mean is the Auto Zeroing or mechanical Zeroing could affect the readings in Unisab II?

[Grizzly]

Hi Tung.
With problem 1.
Have you gone into the setup, whilst the comp is running to confirm the control status?
Also have you or someone else been looking at or altering the unisab wiring?
It does indeed seem strange that you have no shutdown.
Just how long are you depressing the control button?
Problem 2.
Basically when the unisab sees no movement of the capacity slide within the preset capacity error fault time.

(Which from memory is something like 30 minutes although this can be altered. The Capacity error alarm will show.)
This means that whilst running the unisab expects to see a fluctuation in load.
And if the slide does not move within the alloted time for whatever reason.
The unisab will shut down on this fault.

Various things within the oil / hydraulic loading system can cause these issues.

Don't forget the various oil related service intervals and associated parts that need cleaning / changing.
Not least of all the oil filters and strainer.
All of which can cause load issues.
Your slide position calibration issue has possibly been caused by an incorrect set-up at some stage.
There is calibration offsets available within the software to rectify inaccuracies.
Good Luck Grizzly.

[Tung]

Hi Grizzly,
Thanks for your advice,
as to the problem 1,
I already had brought the Unisab II controller back to my work shop for test, the customer had it replaced by a PLC based controller manufactured by an local electrical engineering company, one of the main reasons for them to did that is because the operators in the plants can't read English,
I have a set of Eproms and Par of Version 2.04 ready for replacement, also I suspect the No.16 relay could have some kind of contact problem, but it has to be replaced by a professional electronic guy if it's defective.

Problem 2,
I have been thinking of this problem since I was back from job site today,
I noticed when compressor shutdowns, the capacity slide sometimes won't be able to fully unload to the real 0% position(get stuck due to some mechanical problem), there is about 10 degrees difference, so I guess when I did the zeroing, the actual position of capacity slide could be 10 or 15%, just when the compressor start for a while, the increasing discharge pressure will push it back to its minimum position and the indication at the time of course would drop to minus,
I think it is better for me to solve the slide valve's mechanical problem first, otherwise I will never get a correct adjustment.
I have set the calibration offset both(0% & 100%) to 0.

[Tung]

Sorry, some mistake,
the discharge pressure built in Sab202 compressor will help on pushing the slide vave to loading direction,
not unloading.

[Josip]

Hi, Tung :)


Hi Grizzly,
Thanks for your advice,
as to the problem 1,
I already had brought the Unisab II controller back to my work shop for test, the customer had it replaced by a PLC based controller manufactured by an local electrical engineering company, one of the main reasons for them to did that is because the operators in the plants can't read English,
I have a set of Eproms and Par of Version 2.04 ready for replacement, also I suspect the No.16 relay could have some kind of contact problem, but it has to be replaced by a professional electronic guy if it's defective.

Problem 2,
I have been thinking of this problem since I was back from job site today,
I noticed when compressor shutdowns, the capacity slide sometimes won't be able to fully unload to the real 0% position(get stuck due to some mechanical problem), there is about 10 degrees difference, so I guess when I did the zeroing, the actual position of capacity slide could be 10 or 15%, just when the compressor start for a while, the increasing discharge pressure will push it back to its minimum position and the indication at the time of course would drop to minus,
I think it is better for me to solve the slide valve's mechanical problem first, otherwise I will never get a correct adjustment.
I have set the calibration offset both(0% & 100%) to 0.

Regarding problem 1 ... first check wiring-must not be possible to start compressor automatically in manual mode, but maybe you have some remote switch overriding this ... someone maybe altered wiring by chance (I was working in Vietnam and I have some experience with wrong doing work in hurry ;)) ... it is very easy to push the wire into wrong terminal within print board ... also it is possible to have defective contact under 0 button and you cannot stop the compressor or sometimes cannot start or change capacity ... in that case must replace plastic keyboard on the UNISAB, unfortunately, there is no other way to repair it ...

in my opinion, it is not good idea to replace UNISAB with PLC based controller (it can work, but not that good as UNISAB, believe me) ... there is no good replacement due to missing algorithms and subroutines implemented within UNISAB II/III ... regarding operators, it is easy to make a list with translation English/Vietnamese language .... and hang it to UNISAB ... sorry, but for me, operators are little lazy ;) it is much better personal feeling when you can speak or read any foreign language and I know they can learn it ... if not fully, then at least, what is enough for their job ... this is my personal opinion and not intention to offend anyone


regarding relay no. 16 ... you can check it ... try to start compressor with open UNISAB and in the moment when you press I button that should activate red diode-on print ... if not then is better to contact JCI Ref.

I'm not sure how you can check UNISAB in the workshop if it is not connected to sensors (we perform such activities directly on site i.e. compressor), but maybe you have some good way to do it ...

Regarding problem 2 ... first you have to check capacity and Vi slide for free mechanical movement (you must remove discharge cover to take out capacity slide and check both: capacity piston&teflon ring and cylinder ... assuming that you have manual Vi slide you need to setup it (using diagrams according to your compressor, refrigerant and suction/discharge pressure when compressor is off) before you attempt to setup turning capacity sensor .... in case you have some problems with slide movement after some time UNISAB will issue capacity error signal and stop compressor ... same as explained by Grizzly

there are very good instructions how to perform capacity sensor setup within SAB 202 manual or UNISAB II manual. Of course, if the old one is damged you need to replace it, but again you have to setup 0% capacity position-with zero screw when compressor is in minimum capacity and 100%capacity position with-span screw when compressor is in maximum capacity .... this you can check with ampere meter ... if you press increase button in manual mode and there is no change in consumption that means you are in maximum capacity...

I had some problems to setup the same type of capacity sensor (turning model), but finally we did it .... don't worry if the hand on capacity sensor is not in exact position it is only for visual information to operator ... important is output signal to UNISAB II when compressor is in min/max position to not issue any further signal to decrease i.e. increase capacity when compressor is in one of those two position ..

Hope this is of some help to you.

Best regards, Josip :)

[Tung]

Hi Josip,
I appreciate your advice on this issue,
as to the problem 2, I still think the stuck slide valve is the first thing I have to get it done,
and this Thursday I will try to take the SV out and inspect what is going wrong there inside the compressor, before I had another Sab202 that the SV was stuck in discharge ports, but this case is somewhat different, the SV is stuck in a certain position when unloading, when I restart the compressor then after the discharge pressure is built up to 11.5 Bars without loading command, the SV will be pushed to its minimun position and that causes my previous zeroing failed,
anyway I will be able to know what causes the SV stuck and hope it is not too serious that could lead to further disassembly to the whole compressor,
again thanks for your valuable advice.

Tung

[Tycho]

I learned this today, and I will share it with you :)

on the sab 202 with auto Vi it has a mechanical 0% which you calibrate with the zero screw on the indicator while the compressor is not running.
When the compressor starts, it will go to a calculated 0% which is around 25% higher than the mechanical 0% (it can vary), so during startup, it will show a negative cap (not sure how long) then the cap slide will move to the calculated 0% (or as you say 10 degrees over mechanical 0%) and the unisab will show this as 0% in the display, if you go to setup->calibrate->capacity, you can see the real mechanical position of the cap slide, the one displayed in the normal menus is a calculated capacity, and not the real position of the slide.

here is the user manual for the unisab II if you need it http://www.scribd.com/doc/57345616/Unisab-II-0178-445-ENG-logo-1 see page 99 and 127 for how the regulator works, and how to calibrate.

also see my post at http://www.refrigeration-engineer.com/forums/showthread.php?36767-SAB-202S-cap-and-Vi-slide-headache in case you have any input :)

[Tung]

Hi Tycho,
Sorry for replying late as for the last whole week I had been busy on T/C job for a refrigeration plant on a fishing boat,
this Sab202 I dealed with has fixed VI, before I went away, I have took off the slide valve and discharge casing, the C-Ring on piston is worn seriously, it has to be replaced, and the cylinder in discharge casing also has some scratches and I have them grinded to the best condition I can give,
I will return job site to install the new C-Ring and test the movement of slide valve tomorrow,
hope this time I can make a satisfactory seat.

[Tung]

One additional question,
if the position transmitter is totally out of range,
do I have to apply the 24 VDC to the transmitter when doing the out-of-range adjustmemt?
please refer to the attached file on page 2.

[Josip]

Hi, Tung :)


One additional question,
if the position transmitter is totally out of range,
do I have to apply the 24 VDC to the transmitter when doing the out-of-range adjustmemt?
please refer to the attached file on page 2.

Seems transmitter must be connected to UNISAB II otherwise you cannot see when you have 0% capacity;)

... but not sure how you can check voltage according to this manual it is applied only to Prosab II and Unisab-S control devices ... also what is important is instrument batch number ....

for Unisab II we have terminals where you can check terminal 29(24V) and 31 (SIG) terminal 30 (GND), between terminals 30/31 is resistor of 250 Ohms

Attached is one file with adjustment ....


Best regards, Josip :)