Calibrate a densitometer?

[Matthew Rolfe]

Hi

Is there a simple and easy way to calibrate a densitometer? Any suggestions?

Thanks

[Marko]

Hi Matthew,

The exact procedure depends on the model. But essentially, there are two steps to it:

1. Set the zero point - take a reading with no film, just the light itself and set the scale to zero. If your model comes with separate color channels and a composite one, zero out each channel.

2. Calibrate to a known standard - measure a previously calibrated sample and set the instrument to that value. Normally, it would be the "calibration chip" that originally came with the device, but if you don't have it, you can order a calibrated transmissive wedge from Stouffer and use the densest step for this.

Recommended practice is to turn the densitometer on at least one hour prior to use (to let the light source filaments to heat up and stabilize) and to calibrate before each session.

Hope this helps.

Marko

[D. Bryant]

Hi

Is there a simple and easy way to calibrate a densitometer? Any suggestions?

Thanks

You really need the manufacturers calibration references for reflective and/or transmissive readings to ensure you get consistent readings and to know that your instrument is working properly.

At the very least get a copy of the instruction manual and purchase a Stouffer's calibrated (reflection and/or transmission) step tablet with the proper density range required for calibrating your machine.

Don Bryant

[ic-racer]

A generic calibrated step wedge is a little on the expensive side, but it will have an appropriate density strip that can be used for the "high density" calibration. On my unit it specifies using a density standard around 1.8 log d.

Which densitometer do you have? If you don't have the manual, maybe someone can help you out.

[Matthew Rolfe]

Marko, Don and IC, thankyou for your responses.

I don't have the instruction manual or the calibration chip so I am a bit stuck there. The make and model is;

Melico PhotoLog B/W Transmission

I will have a look for the manual on the internet. I will have a look at the step wedges, prices etc, I hadn't heard of them until you replied to my post, so thanks for bringing them to my attention.

[Marko]

WFIW, I am using Stouffer TP4x5-21C step wedge, which stands for Transmissive Projection 4x5 21-step Calibrated with the Eseco TRC-60D densitometer. Here's the link:

http://www.stouffer.net/Productlist.htm

The important part is to get the Calibrated version (a C version) rather than non-calibrated, even though it is a bit more expensive (but still very reasonable).

I bought my densitometer on eBay for a song, but it came with no manual and no calibration chip. I tried buying the missing parts from Eseco first, but they didn't seem at all interested and at my insistence quoted a truly ridiculous price.

Stouffer, on the other hand, was very reasonable and nice to deal with. I got the manual for free from another member, and it's been working fine ever since.

Marko

[TKCheah]

Dear my friends,

I have a GAM densitometer standard. (Reflection densitometer)

Please share with where should I send the standard sample for re-certificate.

I can be contacted by tkcheah@pioneerstd-ap.com

[ic-racer]

I'd just buy a new sample if you think yours is no longer correct.

[Peter De Smidt]

X-rite makes calibration plates for reflection densitometers. Another option would be to someone who has a good reflection densitometer, as well has the correct calibration plates, takes readings of your plates. You would then know the numbers that you'd need to enter into your densitometer to use your plates for the calibration routine.

[TKCheah]

Dear Peter,
I'm from service company. The densitometer belong to customer.
They requested to do re-certification on the standard plate.

I guess confirmation with a good densitometer may not acceptable as they was requested by the auditor to re-certify the standard sample.
Do you know someone can do re-certification for this standard sample 139722?

I get your idea, maybe look for X-rite to get a new calibration plate.


X-rite makes calibration plates for reflection densitometers. Another option would be to someone who has a good reflection densitometer, as well has the correct calibration plates, takes readings of your plates. You would then know the numbers that you'd need to enter into your densitometer to use your plates for the calibration routine.

[neil poulsen]

All the calibration means for Stouffer step wedges, is that they've read the steps with a densitometer that's traceable to the national standard. The readings are written down on the envelope that holds the wedge.

Stouffer's makes an economical five step wedge (including film base plus fog) that will work fine. This wedge also includes readings near 1, 2, 3, and 4. (The fb+f reading will be about 0.05.)

After zeroing, I adjust the slope setting so that the densitometer correctly reads the "3" wedge, and I also check to make sure that the readings of the "1", "2", and "4" steps are appropriate. After this, I may check the zero again, and if I change it at all, I would recheck the slope setting.

[TKCheah]

Good Morning,

I had got the standard from Tobias Associates, Inc.
The Black and White standard was little different from the original standard.
(Refer to attachment on the standard value)
But I was stuck with the as I do not know how to key in the value of the standard.

Can someone help or maybe share with me on the operating manual for this model.
(Refer to attachment on the machine photo)


141551

[Bill Burk]

TKChea, you have the new standard in hand valid through September 30, 2016. This may be what you were brought in to provide: A certified standard.

The people who use the densitometer must have been following a calibration checking procedure which would be fairly straightforward. Set the channel for Black, Yellow, Magenta or Cyan and read the white patch. Turn the knob for that color channel (knob marked "zero") until you get the reading under the zero column of the standard for that channel. For example the black channel, should zero to 0.010 on the display when reading the white patch. This is safe to do because you are not "calibrating" at this point, you are just adjusting zero which is part of normal operation. That's why it's a big knob.

You can safely check the densitometer calibration. Read the standard black sample with the black channel selected and look for a reading of 1.610 on the display. Write down the reading you get on a report. Do the same for the other three color channels.

I hesitate to calibrate even my own densitometers because I don't know if I will mess it up.

To reiterate, until you get a user or service manual, change nothing inside the densitometer and just read all the samples and write all the current values displayed on the densitometer without making screwdriver adjustments...

If the readings are only a small amount (+/- 0.100) off the samples it may not be necessary to calibrate. Remember if the shop is trying to print a standard quality and you change their densitometer, they may meet external standards after your change... but the jump in appearance may be objectionable in-house.

If the readings are very far from the markings on the samples, this may mean somebody did play with the screwdriver adjustments. Then you might be forced into saying the machine has been tampered with and should not be trusted.

The screwdriver adjustments are used to set the high readings to match the color sample for the color channel. But they should be done following manufacturer instructions, not an internet expert.