I suggest to put a black paper sheet inside the compartment. The window of the light beam should be covered

Hi Francisco.

Thanks for the suggestion. I gave it a try but this time the startup stopped before it reached to "Checking dark cvalues test". It gave me another error - "Beam blocked".

Any other thoughts?

Regards,

Richard

Assuming that the message is correct, it sounds like you have a light leak into the compartment.  To test this idea get a black cloth and wrap the machine in it, pull down the blinds and turn out the room lights then rerun the test.  If that solves the problem try blocking the light in different locations.  If it doesn't solve the problem you need a service call.

Michael - I assume its just using the normal detector. It runs through a test of both the UV and Vis lamps which then turn off and the dark value test is then run. There is nothing else in the compartment itself.

Even though the error occurs, the device still functions to a point. I can make measurements but there seems to be a bit more noise than expected.

Paul - Yes, I had that idea. I have yet to try it. As far as service calls go, the model is outdated and the manufacturer was bought out by another company. They weren't terribly helpful.

The problem may be non-zero (uncompensated) dark current of the light detector.

Thanks Peter & Joseph. Not really what I wanted to hear.

I'll give the high voltage if the device allows me to.

Dear Richard Symes

How many hours of operation this spectrophotometer?

It is possible that the photomultiplier device may be worn. Easy to replace.

Good look

MI

Hi Richard,

I don't know this specific type of UVvis, but very often a so called shutter is blocking the light in the compartment. The reason is that you do not want your sample to be exposed tp the light all the time, but only during a measurement. Maybe this device got stuck (partially). It is probably also this device that switched in and out the lightpath during boot-up of the instrument and let you know that the beam is blocked (or not).

Is this a conventional UVvis or a diode array spectrometer ?

If conventional indeed the PMT might be defect

This is  unusual observation Only solution is to give appropriate correction to the absorbance value by correcting readings for the blank

Dear Richard Symes

Sorry for the answer; since yesterday.

I studied and has photomultiplier device.

It is equipped with a single silicon photodiode solid state.

I think it should be replaced or amplifier circuit.

Good look

MI

Thanks for the information, Mihai

PMT are highly sensitive to UV and visible radiation. The sensitivity of an instrument with PMT is limited by its dark-current emission. They are limited to measuring low-power radiation because intense light causes irreversible damage to the photoelectric surface. For this reason, the device should always housed in a light-tight compartment, and care should be taken to eliminate the possibility of its being exposed even momentarily to daylight or other strong light.

Richard, this could explain the lack of sensitivity you noticed. As Peter mentioned, it seems to be a symptom of PMT failure.

You have not read the instruction for Sp.

Hi Vladimir.

Unfortunately I don't have the instruction manual. I can't find it online.