another idea to put the DMCheck Plus in a box - Page 1
Forum section: electronics / testgear

author: unicornio
author_rank: Contributor
timestamp: June 21, 2014, 12:11:49 am
content: hi guys!finally I have my DMM Check Plus!!!I think Doug Malone has had a good idea, and his development has gotten to a optimum level of quality and reliability at a cheap option. the precision and acuracy that sends us from his small craft production can help us a lot to maintain confidence in our multimeters, oscilloscopes and some other meters.Here we live in the mountains and we have a repair shop for solar energy systems (powered with solar energy too) and we need a certain degree of accuracy in the measurements we do, but we do not need to follow a annual calibration program of instrumentation, and we can save a lot of money and time if we know that our multimeters are working without needed to sending it, which can even be damaged, out of adjustment or even lost in the shipping transit...to accommodate the DMMCheck Plus, I chose a luxurious wooden box that held (one day) a set of precision microwave attenuators from hp. I have tried to be less traumatic for the PCB that Doug sent me, so I just modified it essential to be able to handle with ease and comfort, ensuring that the DMMCheck Plus is very wel protected.connections on the outside, as you can see, are very old banana type, of Bakelite, which I use with Pomona probes, also very old.connections inside are very short and are made with gold plated pins used in radio frequency circuits.at the top of the box fits perfectly the document that Doug sent me, in which he points the results of their measures with their traceable calibration instruments.the result can be seen with both flukes, 87III (15years) 8050A (25Years) and taiwanese (Lutron) Fake fluke 8020 (30Years)all of them are within their limits of accuracy, so we no need rid of them or send them anywhere.i want to put here some images:

author: AlfBaz
author_rank: Super Contributor
timestamp: June 21, 2014, 01:52:52 am
content: Nice, but wouldn't soldering to those precision resistors (thermal cycling) change their values somewhat?

author: unicornio
author_rank: Contributor
timestamp: June 21, 2014, 11:51:43 am
content: Quote from: AlfBaz on June 21, 2014, 01:52:52 amthanks so much for your post.All welds that have been made on the PCB of the DMMCheck Plus, have been made with a soldering tinny tip and with a weller soldering station with ESD protection, and with a 'fluidel 5 trimetal 0,5mm tin wire'. instead welds on the 'bannana' connectors, that have become soldering apart, with a 60w weller with a thick tip.before touching the DMMCheck Plus, I have taken note of all the steps and measures, to check if there was any change before boxing it, and yes, there have been some very *very* slight changes in resistance measurements, but I put this down more to the change of the connection point along resistor terminal, nor to the heat received by resistors, which at least, are made to be welded.anyway, I will discuss this with Doug, to see that thinks of all this. maybe the form that Doug gave to the terminals of the resitors was to prevent that them are affected to the welding temperature, and I thought it was just to facilitate contact for use and measurement ...meanwhile, now the connection with the series of resisstors is fixed and firm, much more stable and precise, so that no longer will be no changes due to the connection point as there would be if we used the DMMCheck PLus in their original format without box with a alligator clips. thus now the measures will have a better repeatability and simplest, and the measure can be easily always the same.however, this must be taken into account, it is very important: when we re-send to Doug our DMMCheck Plus for recalibrate, even he will use the same Pomona probes that we will use, because we will send these test probes to him, so that once re-measured and recalibrated, our DMMCheck Plus will be a unit with more stability, more accuracy, and more easy and convenient to use ...really, when you have the bare PCB DMMCheck Plus in your hands, and you have to use it, it is very difficult to make the connections, because it is so inestable and easily moved, and is very scary fingering it ... ;-)

author: AlfBaz
author_rank: Super Contributor
timestamp: June 22, 2014, 02:33:36 am
content: Quote from: unicornio on June 21, 2014, 11:51:43 amOk if you are doing that then no problems. I have one of these units and the paper work that comes with it has Doug's measurements at a defined calibration temperature with his 3458. I presume the measurements are made on the completed, aged (ovenised) unitI'm not 100% sure about permanent changes to resistors due to the soldering process, but I remember reading somewhere that depending on the type of resistor (carbon, metal film, foil, wire wound etc) there are changes made to the internal structure of the resistor material by varying amounts. It might not be much but we are talking about a transfer standard that relies on recorded measurement dataI just did a quick test on a 10ohm 1% 1/2watt metal film axial resistor. before soldering an average reading of 9.9483 ohms, after placing some solder on the leads with the iron set at 350 deg C I got an average of 9.9568 (after letting the resistor cool down). Not a huge difference but a difference none the less

author: saturation
author_rank: Super Contributor
timestamp: June 22, 2014, 01:22:11 pm
content: The boxing of the electronics is nicely done. Its more helpful to box voltage references in a metal chassis to act as a faraday cage; this reduces the pickup of stray EMF [e.g. radio waves, wifi, cell phones] that impinge on the PCB or wiring and produce a lot of noise in the uV, uA and milliohm resolution; much worse is static build up if plastic is used in the case. If the reference is used mainly to check 4.5 digits DMM like devices, its less a concern.

author: unicornio
author_rank: Contributor
timestamp: July 01, 2014, 11:20:48 pm
content: hi, there, and many thaks for your post!Quote from: AlfBaz on June 22, 2014, 02:33:36 amI'm not sure if Doug 'get older' their DMM Check Plus with high temperature (in an oven, which is called 'climate cycle'), nor he only 'burn' it having them running hundreds of hours working at room temperature.Quote from: AlfBaz on June 22, 2014, 02:33:36 amas the Dalai Lama says,everything changes,nothing stays!...;-)Quote from: saturation on June 22, 2014, 01:22:11 pmthanks so much, I'm glad you like.Quote from: saturation on June 22, 2014, 01:22:11 pmI have not taken into account all interactions on rf. here we have a fairly clean environment, but in such operations is better be aware of these issues, since the cables used are 'so long' and without any shielding protection...;-)