WTB high resistance decade substituter (US) - Page 1
Forum section: electronics / general

author: itsbiodiversity
author_rank: Regular Contributor
timestamp: February 10, 2021, 01:18:20 am
content: Looking for an accurate high resistance >10MOhms upward to 1Gohm. Anything out there. I do see Time electronics has a small 100 Mohm model.

author: itsbiodiversity
author_rank: Regular Contributor
timestamp: February 17, 2021, 01:00:25 am
content: Any help here? Should I just build a decade resistor with some Ohmite high voltage resistors or buy the IET model?

author: bob91343
author_rank: Super Contributor
timestamp: February 17, 2021, 01:53:57 am
content: Building is usually better.I have a couple of GR decade boxes. They are very accurate. Other than testing Ohmmeters I don't have a use for them.

author: jfphp
author_rank: Regular Contributor
timestamp: February 17, 2021, 06:32:37 pm
content: What exactly do you want ? Resistors alone 1Mohm, 10, 100, 1T, 10T... or X to 10, 100 Mohm ... in decade steps ?

author: srb1954
author_rank: Super Contributor
timestamp: February 18, 2021, 12:59:42 am
content: Quote from: itsbiodiversity on February 10, 2021, 01:18:20 amLooking for a decade resistor up to 1Gohm is going to severely restrict the available options in commercial products.A better approach might be to make your own decades for the range 10Mohm upwards and use a commercial decade box for the lower decades. High value thick film resistors are available reasonably cheaply but generally only down to tolerances of 1%. You may require some selection or padding of resistors if you are looking for closer tolerances than 1%.

author: jfphp
author_rank: Regular Contributor
timestamp: February 18, 2021, 05:03:17 pm
content: Custom high value resistance box : if you are interested...

author: TimFox
author_rank: Super Contributor
timestamp: February 18, 2021, 06:07:07 pm
content: A quick note on "usage", which might help your search:A "substitution box" is usually a relatively simple unit, covering a range of values, but with only medium resolution and accuracy. This Extech unit is an example:https://www.grainger.com/product/40JZ72?gclid=EAIaIQobChMI9Ji1uIL07gIVE77ACh3LtARgEAQYAyABEgLMNvD_BwE&ef_id=EAIaIQobChMI9Ji1uIL07gIVE77ACh3LtARgEAQYAyABEgLMNvD_BwE:G:s&s_kwcid=AL!2966!3!264955916564!!!g!442140938772!&gucid=N:N:PS:Paid:GGL:CSM-2295:4P7A1P:20501231Substitution boxes are useful when you need to quickly try different component values, for example a capacitor box to test compensation networks in servos/feedback amps.A "decade box" is usually more expensive, containing higher-accuracy components. The classic General Radio resistor decades are a good example, now available from IET:https://www.ietlabs.com/1433.htmlIIET also makes less expensive substitution boxes.

author: itsbiodiversity
author_rank: Regular Contributor
timestamp: February 19, 2021, 10:55:33 pm
content: I have high accuracy resistance available up to 10 MOhm; however, some cal procedures call for values upwards of 200 MOhms at 1% accuracy. That is what the box would be used for.

author: Vgkid
author_rank: Super Contributor
timestamp: February 20, 2021, 02:21:54 am
content: When I was looking around earlier, most on ebay don't offer great accuracy, though the Yokogawa ones do. They are just really expensive. Most ceramic switches offer good insulation, so a DIY would be good. Depending on accuracy it could get expensive .