MCCNC troubleshooting » Historique » Version 38
- OPC flooded or dirty
- No counting
- Flow rates
- Related pages
When the available space on the mCCNC flash disk goes low, the firmware will print an alarm message. Then, when the disk is full, it will eventually stop running. To fix this, see clear CF data.
The firmware won't start¶
The firmware starts, displays an error like "cannot open file" in the console and quits straight away. This is a bug due to a limitation in PicoDOS : the number of files in a directory cannot exceed 512.
Workaround : delete the data files or move them to a sub-directory.
Note : this should not happen in newer versions of the firmware, since data are saved in subdirectories under C:\.
OPC flooded or dirty¶
The scatter value is larger than 2000mV¶The OPC is probably flooded. Try these operations in the following order :
- Start a drain sequence.
- Run the mCCNC in dry mode.
- If the scatter stays this high, open the OPC and blow the water with a gentle flow of dry clean air.
If it doesn't help, open the OPC and wipe the spherical mirror, the slotted golden plate on the laser side, and the lens VERY GENTLY with a wet cotton swab / Q-tip. Use ONLY WATER.
See also The drain doesn't work
The drain doesn't work¶
The drain pump may need to be primed ; it is not self-priming. In other words, the drain won't work if the tubing between the OPC and the drain solenoid pump contains too much air. Remove the column, start the mCCNC in drain mode, and push water with a syringe into the manifold port closest to the PCB stack. Check that water disappears from the manifold port when the mCCNC runs in drain mode.
The OPC gets repeatedly flooded¶
After draining and running in dry mode, the OPC scatter drops bellow 1600mV and the mCCNC counts particle. But the OPC is flooded again after running for a couple of hours.
The check valves in the drain solenoid pump may be worn out and leak. The pump is not as efficient, and can't evacuate the excess water from the OPC anymore. Replace the check valves.
High scatter, dry OPC¶
If the OPC is dry and the scatter remains higher than 2000mV, then the OPC is probably dirty. Remove the parabolic mirror, and clean it with a cotton swab and deionized water, along with the slotted mirror and the hemispherical lens in front of the detector. Use a black permanent marker to make the capillary from the column totally black. If the problem remains, clean the lens in front of the laser is probably dirty.
Cleaning the lens in front of the laser, is a delicate operation that requires special training.
The mCCNC does not count particles / the firmware stops after 1 s¶Check the connections of the column :
- The Sub-D plug connects to the header attached to the side of the case.
- The SMB plug (golden coaxial connector) connects to the INPUT socket on the OPC amplifier PCB. The TTL socket on this PCB is the output of the amplifier. This wire goes to the PCB stack. Nothing connects to the HP socket.
Out of water¶
Check the water level through the window on the side opposite to the connectors. Fill the water reservoir if needed. When the mCCNC has run out of water, the column has to be primed.
When the mCCNC has not been used for a long time, or has run out of water, the column has to be primed, i.e. it must be saturated with water. To do so, start the mCCNC in prime mode. The firmware will automatically stop after about 5 min. Then, run the mCCNC in normal mode, and check if the concentration increases to at least 300 #/cm 3. It may be necessary to repeat the operation several times.
Flooded frit (advanced users)¶
The frit in the head of the column may be flooded. This frit is used to laminarize the sheath flow. If it is flooded, the sheath flow stream won't be uniform down the column. This will cause particles to hit the walls, instead of falling straight into the OPC.
Take the frit out of the head, blow dry air in the small duct and wipe up water at the same time.
See also : The water cannot reach the column
The water cannot reach the column¶
Check if the water can flow up to the column. The fill pump may need to be primed (it is not self-priming) or a bubble has formed in the tubing.
- Make sure that the water reservoir is not empty.
- Remove the column off the manifold and connect a syringe to the Manifold, port 7.
- Start the mCCNC in prime mode, while pulling with the syringe, so as to create vacuum.
- Wait until water comes out of the manifold port.
- Start the mCCNC in normal mode.
No counting and scatter very low¶
If the scatter is much lower than 1000 mV (normal scatter range is 1000..2500 mV), the coaxial connectors on the OPC amplifier PCB may have been swapped.
Check the OPC output¶
Check the analog pulses, the electrical signal from the OPC, with an oscilloscope. If the pulses are much lower, wider and noisier, check the laser position. The cross section of the laser case is rectangular ; the laser must be mounted so that the longer dimension is horizontal when the column is in the upright position.
Check the OPC threshold¶
The OPC threshold was adjusted during OPC calibration. This is kind of a factory setting. The threshold is set with potentiometer R6 on the OPC amplifier board. The potentiometer may need to be adjusted or replaced (see the spare parts section).
The values for each device can be found in the hardware section.
The S/A flow rate ratio is out of limits¶
Adjust the variable orifices on the side of the mCCNC.
Perform a Leak check.
Flows don't start¶
The flows are controlled by normally closed, proportional valves (PV). They are drawn in red on the schematic diagram. The PV closest to the column takes air from the column and is the lower one on the diagram. The second one controls the make-up air directly from the inlet.
They both connect to a 20-pin connector on the lower side of the power PCB. The 1st one connects to pins 15-16. The 2nd one connects to pins 13-14.
- Check contact failure : disconnect the header and measure the electrical resistance of the coils (68R).
- Check if the valves open when powered :
- Connect a vacuum hand-pump in the place of the membrane pump.
- Evacuate to create a small vacuum.
- Apply 12VDC to one of the PV. Polarity doesn't matter.
- Check the vacuum : the pressure should return to ambient immediately.
- Repeat for the 2nd PV.