Part 2 posted here where it will get some views
This will cover the 2450 as a Power supply, Voltmeter, Ammeter, and Ohmmeter. I show how the 2450 specifications compare with the Agilent B2901A SMU, my Fluke 8846A and my IET LOM510A micro-Ohmeter. The last two are the only calibrated instruments I have to do accuracy comparisons with. The Agilent B2901A is a close match at $500.00 more than the 2450 and is higher performance in several areas but is less accurate on paper. All the specs have been charted in a way that graphically show where each instrument is most accurate. The measurement comparison charts have a spec ratio column that show which instrument should be the reference and how much more accurate it is. I include the ancient HP6115A power supply in the power supply testing since its specs are very close to the 2450 and even better in some parts of the ranges. This 6115 is as received from fleabay with its last calibration in 1992. There are lots of things a metrologist would pick apart about my comparisons but I am just trying to give a general feel about how this unit performs. 2450 readings were done at 10NPLC and a repeat filter of 10 and then stat average using the number of readings show on each chart. The 8846A was set for 100NPLC and a stat average of the number of readings show on each chart. This was done to minimize noise and give stable readings at these high resolutions. 8846A accuracy is the same on 10 and 100NPLC
I have used the touch screen even more in doing this testing and I really love this interface. I can’t think of a more efficient system for entering settings. The milli, micro, nano, x10, and /10 buttons on the input screen are absolutely brilliant. I have found I rarely want to use the navigation knob even though it works well. This screen pops up for both voltage and current settings/limits.
Use as a power supply in Voltage mode and as a Voltmeter:This is the stat screen of sourcing 1mV for 101 readings (roughly 6 mins). Notice the 10nV resolution and a span of 170nV and SD of 31nV. This is pretty good stability in my book.
This is the stat screen of shorted input and zeroed with relative function for 658 readings (roughly 36 mins). Notice the span of 210nV and SD of 37nV. Only slightly higher span and SD than the 6 mins above.
This is the response of changing the voltage value from 1V to 5V and back to 1V with no load. Nicely behaved
This is the output switch on and off with a 5V setting. Also well behaved. Notice the approximately twice as fast rise time compared to the voltage change above.
Some points on all the spec charting:These are plots of the 1 year specs of maximum error as a
percent of the measured value. This puts all specs on an even playing field for comparison. The jagged data jumps are the natural effect of (% of reading + offset or % of range) at the range changes where percentage and/or offset values may be different. The other subtle data kinks are the effect of the value data not being the same step in value from decade to decade. What appear to be discontinuities of data from one chart edge to the next is a range jump happening right on the chart edge.
The SMU’s are very close and better than the 6115A in this range. The 8846A is over 40x more accurate than the other instruments in this range up to 10mV and progresses to 2.2x more accurate at the 200V level. This makes it the reference for all measurements in all ranges on the voltage testing. Unfortunately it won’t be that clear cut on current and resistance comparisons.
The 2450 and the 6115A are significantly more accurate than the 2901A in the 2 to 20V range.
The 2450 and the 6115A are significantly more accurate than the 2901A in the 20 to 200V range. The 6115A even beats the 2450 measure spec in the 20 to 80V range.
A little guidance on this mess. All the blue columns are 1 year specs in ±volts for each value. The yellow column is how much more accurate the 8846A is compared to the 2450 measure for each value. The light green columns show how much percentage of the spec is used if the 8846A had no error. To go to the other extreme, in the magenta column I ignore the extremely good 8846A Cal. data and add the full 8846A spec error to the instrument error and use that to calculate the worst case percentage of spec used. In both cases the percentage of spec used is impressively low. The 6115A was last calibrated in 1992 and is still in spec (also very impressive). I used 2 short coax cables with 4 coax to male banana adapters to connect with remote sense right at the 8846 input terminals. I think the outer shields of the coax being connected to the 8846A measurement common helped the noise be lower than using 4 independent banana jumpers.
Use as a power supply in Current mode and as an Ammeter: This is a stat screen of sourcing zero current thru Force high and Force low triax cables that are connected at one end The measure reading was zeroed out using relative. A span of 110fA and a SD of 19.7fA over 62 readings is amazing. You can’t get here without the triax and driven guarding of the rear terminals.
With current things get a little more complicated. The 8846A is only equal or more accurate in the 1A to 100mA range. After that the 2450 is progressively more accurate as the measurements get lower. At 10nA and below the 2450 is approximately 500X more accurate than the 8846A. Another area where the 2450 excels in current measurement is its very low burden voltage of ?100µV on all ranges.
Clearly the 2450 excells here and is more accurate than the 2901A in the 110pV thru 1A range. The 2901A does not have separate source and measure accuracies. On the 2450 with source readback on, the sourced value is measured at measurement spec accuracies before it displayed and used in any calculations such as resistance or wattage measurements. This is an example of how difficult spec comparison would be without this chart style. Look at how the 2450 source and 8846A 10NPLC cross over each other multiple times on which is more accurate.
The color coding here and chart explanation is the same as the similar Voltage chart above. This is the accuracy measurements where the 8846A is the reference. Obviously you have to take the spec ratio into account as to how much weight you give to specific values. This was done with Force high and Force low triax cables directly feeding the 8846A in current mode. Considering the last Cal data of the 8846A it is reasonable to use the “error as percent of spec assuming no error on the 8846A” column as a general measure of accuracy. Very nice results with a high of only using 8.6% of the allowable spec. Even if you use the magenta worst case column it is still well within spec.
These are the accuracy measurements where the 2450 is the reference. Again you have to take the spec ratio into account as to how much weight you give to specific values. But the 2450 is clearly the reference here. The 1.2 and 1.3 ratios seem to be anomalies but they are cause by the 8846A having 20% over range where the 2450 has a 5% over range. This is most noticeable where the spec ratio is less than 1.5 but exists in all the ratios. The offset or % of range part of the specs has the least effect at the top of the ranges. The measurements at 100nA and below were done with both the 8846A and 2450 offset currents removed with relative or zero. The 2450 worst case source error as a percent of spec is all within tolerance even when adding the full measure spec error to the measured value. The 8846A also does very well with very low percentage of spec numbers especially below 100µA.
Use as an Ohmmeter:Quickset gets you to ohmmeter and allows setting 4 wire mode. For maximum accuracy source readback needs to be on and offset compensation needs to be on for low resistances to minimize the effects of thermal emf’s. This chart shows the LOM510 is clearly the reference for 2 ohms and below. The 2450 has better resistance specs than the 2901A in all ranges.
Here we see the 8846A is clearly the reference from 20 Ohm to 10M Ohm
All the 2450 resistance measurements were done using using full 4 wire triax kelvin connections to the resistances. Source readback was enabled along with offset compensation. The <2? values were done sourcing 1 amp. The 8846A was also 4 wire kelvin connections and offset compensation on the low values using my offset compensated ohms adapter. The IET LOM510A is 4 wire kelvin connections and used the offset compensated ohms mode. The resistances from .1? to 20M? were my .1% decade box. The three lowest resistances was a piece of wire with the sense connection spacing adjusted to give the nominal value as measured by the LOM510A. The spec ratio of the LOM510A on these values is certainly high enough for this to be a valid method. My connection system allowed me to connect each instrument to the setup without disturbing the exact spacing of the 4 kelvin clips. This chart is strictly a general comparison using the best spec instrument as the reference for the relative accuracy of the other two. The best spec instrument is dark blue background with the second best spec instrument in light blue background and the worst spec instrument with no background. All I can say here is all the instruments agree pretty closely and generally do much better than their one year spec. I finally realized the 2450 has a fan that kicked in when sourcing the 1A on the low resistances. It’s audible tone says variable speed and its seems to track the demand closely.
Conclusion:I am very impressed with the 2450 performance and ease of use. Entering or changing values is really nice and very quick. The graphing capabilities are very useful as is and I believe will be improved even more with the next firmware release. Even if you could buy separate programmable instruments of equal resolution and accuracy for the same money, I don’t see how it could be as effective as the 2450 with all the built in integration of source, measure and graphing. Since complete test routines can reside on the 2450 it can be a stand alone test and measure unit that can even control external equipment such as binning of components. If you don’t use a SMU for a living there is a lot to learn to really be aware of all the capabilities that are packed into this unit (I am not there yet!). The setup scripts are an important tool to have correct repeatable setups. There are a lot of variables to be set for both source and measure and they don’t get remembered when you turn the unit off unless you store them as scripts and reload them from the usb. This will probably be my most used instrument on the bench because of its extreme versatility.
I will post a video link of general use functionality of all the above source and measure functions in the next couple of weeks,
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