Vishay Precision Resistor Standard - How the Pros make them

5 Jan 2015

I have been working with Vishay Precision Group on the selection of resistors for Current Sensing and feedback divider networks for the OP-Amps control stages for my "Power Supply Project", "DC Load" and "Power Meter", during the conversation I happen to ask about recommendations for resistors to make a Lab Resistor Standard Box for spot checking my lab equipment like DMM's and stated i was going to make a video on the creation of the standard.

VPG have an extensive range of resistors ideally suited for this project and where going to send me some samples to allow me to create a tutorial for making one, these are from the VHP range of Bulk Metal Foil resistors

To my surprise Vishay Precision Group (VPG) offered to make one for me and Richard Zuratt a Senior Engineer with VPG was going to make it happen.

Near the end of December I received my gift from Vishay Precision Group, Hand made Lab Resistor Standard box, a few people asked to have a peek inside so here it is... A quick tear down and explanation on how it is made so you can make your own if you so desire, all the parts are available from Element 14 or other suppliers approved by VPG.

Here is the video

Here is the beautiful finished product, Die cast aluminium box and gold plated binding posts to minimize contact resistance, the pen was not include but gives an indication of the size.

Maximizing economy with functionality by having one side common but effectively all resistors utilizing Kelvin connections

Simplicity is also key, this could have been built with a switch and less binding posts as was my plan but I think Richards approach is way better as there is nothing to wear out

The use of hermetically sealed, Ultra Precision Bulk Film 300mW resistors and in the case of the 1 and 10R Values, OIL Filled, yes I said Oil Filled, wow... all measured to 7 Digits

Even across military temp ranges these only drift by a maximum of 60ppm (TOTAL, not /Deg C), in lab temps, only 10ppm MAX, these resistors are the bees knees when it comes to a lab standard, there not cheap but if you want quality and have the ability to spot check your meters with assurance and not be worrying about the temperature when you do the measurement, these are the resistors for you

The resistors used are the VHP101 (100R - 100K) and VHP202 for the 1 and 10R, the black one at the end is an ultra precision multi chip resistor from Richards private stock that has "Matured over a decade" and is solid as bedrock when it comes to stability (I'm not sure if it is available any more but there are equivalents I'm sure).

If taken care of and not overloaded this standard will be as accurate in 10 or 20 years as it is today.

Links to data sheets

Vishay Bulk Metal Film resistors Home Page: Vishay Precision Group - Foil Resistors - Home Page

VHP101: http://www.vishaypg.com/docs/63003/vhp100.pdf

VHP202: http://www.vishaypg.com/docs/63006/hmetlab.pdf

Excellent attention to detail, take a look at the binding post wiring where the wires are wound around many times before soldering, same for the common bus wire connections