Hi Kim,

Assuming that the NA1500 is ready to go (Ready light is on), and that when
you push the Start button the cycle timer begins to count up, the
electrovalves for the autosampler should energize at the time set on the
Sample Start thumbwheel switch.  

1) The first thing to check is has anyone accidentally pushed down the
"Sample" button in the Manual Exclusion section of the control panel (bottom
row of buttons. That would inhibit the valves from being energized.

2) If the button is not depressed, check if the air is being switched from
port 1 to port 2 at the time set for Sample Start. Remove the two blue
pneumatic tubes which go to the autosampler, from ports 1 and 2. Air should
only be coming out of line 1 if the EA is not running. Put your fingers over
the two ports and start the NA 1500. If the air does not switch completely
from port 1 to 2, and then back to line 1 (at the Sample Stop time), then
either the valves are not being energized or there is a problem with the
valves. 

3) There is a simple test to see if the valves are being energized. Start
the NA 1500, then after the Sample Start time touch a small screwdriver to
the post which goes through the center of the solenoid. If the valve is
energized, there will be a small magnetic attraction. 

4) Next, check to see if the valves are leaking. There is a vent hole on the
electrovalves which allows the air to vent from the autosampler air cylinder
when pressure is applied to one side or the other. Locate the vent hole on
the autosampler EVs (it's in the brass block), and see if any air is
venting. There should be no air leak if the autosampler is not moving. Start
the NA 1500 and when the valves are energized (Sample Start time) check to
see if there is a continuous leak out of the vent when the air is switched
from port 1 to port 2.

If you find the valves are not being energized, there are a couple of
possible causes. One of the wires to the solenoid may not be making good
contact or the EVDV board is malfunctioning. There should be about 24 V
across the solenoid when the valve is energized. 

If there is a continuous leak when air should be switched to line 2 (which
moves the sampler forward), the most likely cause is a crack in the small
plastic gas channeling part which is between the two valves. Instead of
being channeled properly inside the valves, the air goes out the vent and
you don't have enough pressure to drive the air piston forward.

Best regards,
Bruno Lavettre
Costech Analytical Technologies, Inc.             

   

-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf
Of Kim Baublys
Sent: Wednesday, January 18, 2006 5:44 PM
To: [log in to unmask]
Subject: more EA solenoid problems

Hi All,

We have a Carlo Erba NA1500 elemental analyser (attached to an Isoprime) 
and the auto sampler just stopped during an analytical run and will not 
operate even on manual.

By switching the compressed air lines over I can get the auto-sampler to 
close, and then switch lines again and get it to open, which shows that the 
auto sampler is working OK.

This led me to believe that the solenoid valve operating the auto sampler 
was faulty. I have tested all the coils and they have the same resistance 
(150ohms), so I am assuming that the solenoid valve is faulty.  Either that 
or it is not getting the command to operate.

Does this sound like a reasonable assumption?  Has anyone else had this 
problem before? Is there anyway to test the solenoid valve without running 
the furnaces up to temperature?

Any advice welcome.

thanks
kim