Products > Test Equipment
Keithley 2100,2000, etc or Chinese bench multimeters?
Kleinstein:
--- Quote from: Caliaxy on October 28, 2024, 09:58:53 pm ---....
What specs in the data sheets made you infer that KS34465 might have an aged reference (as opposed to KS34461 or SDM3065)?
--- End quote ---
For the 10 V DC range the 34465 specs are 10 ppm for 24 hours, 20 ppm 90 days and 30 ppm for 1 year. So only 10 or 20 ppm of room for drift over 90 days / 1 year.
The specs for the LM399 allow for a typical drift of 20 ppm for the frist 1000 hours. If not preaged this drift part alone would add at least 20 ppm for the first 40 days. To reach the tighter specs it would need some preaging / burn in and possibly also some selection.
A good 6 digit DMM should have some burn in or at least pre-aging of critical parts to get the typical 35 ppm accuracy specs. Without it the LM399 ref. is barely stable enough for this. The meters based on a SD ADC chip have the additional drift part from dividing the reference down for the the ADC and scaling the input signal from 10 V to some 2.5 or 5 V range of the ADC.
Zucca:
--- Quote from: zrq on October 28, 2024, 05:46:56 pm ---K2001 (and M) sometimes appear on ebay for a bit less than $800 so it's indeed a great value meter, but the voltage range noise as tested by myself suggests it's rather disappointing for reading the 7th digit (the noise can hardly be averaged down to 0.1ppm of range).
--- End quote ---
Carefull with cheap K2001 on ebay, they are often corroded by the leaking caps.
Yes it is a bit noisy for a 7.5, but the noise is not due to the HW but for the SW/DAC quantization algorithm.
That said you don't buy the K2001 because of the low/high noise, but for all the rest.
djsb:
Thanks everyone for your replies and general interest.
It looks like I'll be buying a Keithley DMM6500. I'll post back here later when it arrives.
PS, It arrived yesterday morning. I bought a Certified Pre Owned DMM6500 from TestEquity in the UK. It has 3 years guarantee and the calibration runs out June 2025. It came with a cal certificate and still had the plastic screen protector. The instrument was shipped to me from their warehouse in Germany via the UK office in St Asaph in North Wales. The cost was £984 inclusive of VAT and postage. I'm going to be very happy with it.
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