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| Siglent SDM3065X |
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| DaJMasta:
--- Quote from: skander36 on December 08, 2018, 08:15:04 am ---you must add 100-200E for calibration , because there is no means to use this precision device without being calibrated. --- End quote --- It's certainly true with less of a used market the value proposition goes down, but I would pretty strongly disagree with this statement. It your application requires significant measurement accuracy, sure, but you still get all the linearity and resolution of an out-of-cal instrument, and an LM399 is no slouch. While calibration is required for traceability and specific measurement tasks, the majority of uses for a meter don't depend on it, and the likelihood that the meter is going to be out of cal even years after its certificate expires is low, given the architecture. Regarding my 'range advantage' comment, yes, resolution would be the pertinent thing, and while I have not seen a counts equivalent metric for the 34461a and don't know how the ADC ENOB between that and the SDM3065X compares, but if the ADC portion is equivalent, a range setting that is half a competing meter would have double the resolution. Yes dynamic range is important, but with equivalent converters, dynamic range is the same, so the same dynamic range on a full scale measurement that's twice as large means your minimum resolution step is also double the size. Now I don't know if the ADC portions are comparable and don't know if there's enough of a noise floor in the bottom of the range to negate any potential resolution benefits, but while the larger range may be preferable in some applications, the smaller lowest range means the higher resolution on very low measurements. |
| skander36:
--- Quote from: DaJMasta on December 08, 2018, 02:46:39 pm --- but you still get all the linearity and resolution of an out-of-cal instrument, and an LM399 is no slouch. --- End quote --- Can you argue this ? |
| DaJMasta:
What is your measurement requirement? Can you argue that the inherent drift of the reference, the resistors, or the integration cap or something used is enough to realistically cause a problem with your measurements? It takes a demanding measurement requirement to really need it and the majority of instruments that go in for a cal need no adjustment. Your application may require extreme precision, in which case adhering to the calibration cycle and expecting only the specifications on the data sheet are acceptable, but the vast majority of measurement situations don't require that. Keysight has a long history (at least, as Agilent and HP) of instruments that live up to their specification even after their calibration cycles are up, and the 34461a has been around for plenty of time to have its aging characterized. None of this is a slight at the Siglent, which from what I can tell uses very similar parts to maintain its stability and specification, but unless your application requires traceable calibration or absolute accuracy, I don't think there's a compelling argument for keeping an instrument regularly calibrated at a lab. Have some other references as sanity checks and understand how the instrument works, then if anything seems awry you can address it at that time (cal or fix as needed). Sending it in to cal every 2 years when it's not even going to be adjusted unless its out of spec. |
| skander36:
I understand you point of view about the necessity or not about accuracy, but if you can focus on your statement maybe will be more useful for me , i mean technical. I think that if you don't need precision you don't buy 5,5 / 6,5 digit mutimeter . Instead Fluke 87 or even a more cheaper Brymen 869 will be enough . And if you decide to buy SH 6,5 multimeter , you will verify against one with the same specification to find if it still maintain his accuracy . You don't tell me that you will buy a 5,5 digit Agilent and you don't care if it is specifications . Why dont you buy a Brymen then ? |
| DaJMasta:
I have a 6.5 digit meter because I want the precision, even though the accuracy of a 4.5 digit meter would be fine for me. You can use a 6.5 digit meter to measure small scale drift trends, and even when well outside of calibration, it can happily demonstrate that down to at least 5.5 digits or so accurately. That said, since my measurement requirements don't require 6.5 digits of accuracy, letting it drift and be out of cal for a decade or two will still likely be within 5.5 digit meter accuracy spec, which still exceeds my requirements, but will show me all of the fine detail of the nicer meter. I can use my 6.5 digit meter to measure the tempco of a thick film resistor accurately at room temperature - just a few degrees of fluctuation, and that is a useful/fascinating measurement to me that would be tough with a 5.5 digit or less meter. I don't particularly mind if the resistor I'm measuring starts at 101.256k Ohms or 101.254k Ohms (for example), so the calibrated accuracy spec far exceeds my requirements and I trust enough in the architecture, component choice, and testing done by the manufacturer to not be dramatically out of calibration for no reason even well beyond the calibration period. Maybe others don't have the same trust or do demand accuracy or traceability, and it's their choice to make, but for my use-case, a meter that's over-specified for my requirements but is out of cal shows me fine detail lesser meters can't, and is very accurate, even if it's out of its specification. Then if I get my hands on a reference that's been checked against a real standard, or a different 6.5 digit meter in passing or something similar, I can use that as a transfer standard to check my instrument out and verify that at the level of detail I can't otherwise verify on my own, it at least agrees with other instruments. As I've said, It's not the approach for every application or every person, but I think it suits a lot of use cases well. A calibrated instrument does have some extra value, but I don't think it's an inherent requirement for a purchase of a high resolution meter for most people/situations. |
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