Re: Why are there ‘no’ 0.1% 10Meg resistors?

"George Herold" .

Sure I can find a few, but they are mostly out of stock and very expensive. I can get 1% metal film through hole 10M?s for almost nothing.

** When a component is not readily available or is too expensive - you have to use a work-around. This means applying a bit of grey matter.

About 10 years ago I decided to build my own 4.5 digit AC and DC voltmeter using a 20,000 count Datel LED panel meter as the heart.

The look and easy readability of a bright red LED display is way above anything else IMO.

The 4 step input attenuator is a series chain of 1% resistors and 3 x 10 turn cermet trimmers ( totalling a bit over 11 Mohms) - bypassed with close tolerance caps to make the response flat to over 500 kHz.

The chain goes: 3.3M, 3.3M, 3.3M, 220k, 50k trim, 1M, 2 k trim, 100k, 500R trim, 11k. The output points are the wipers of each trim pot and the top of the chain. Took me only a few minutes to set the 3 trims to get within 0.1 % of the needed 10:1 ratios.

The AC ranges are engaged by a relay that brings in an AD536 true RMS to DC converter and the meter is either AC or direct coupled with accuracy better than 1% out to 100kHz on all ranges.

..... Phil

We just barely managed to find some 50M 1% metal film resistors. They're RN55 (1/4 axial) size, so we thru-hole mounted them (at a 45 degree rotation angle!) flying above a bunch of surface-mount parts.

John

They work great though. ;)

Cheers

Phil Hobbs

"George Hairoil"

Still, If I can buy 1%, why won't someone sell me 0.1% for say 20 times more? I wonder if it's a tempco problem. Oh.... I sould look at that.

** You need to look up what the term " tolerance " actually means when applied to Rs and Cs.

.... Phil

They sure don't seem to have much shot noise!

John

"George Hairoil

"Phil Allison"

Excellent! Phil you've got to try some 0.1% (and better) susumu

0805's.

** Not when there are AC and DC voltages of 1kV or more involved.

Go away fool.

.... Phil

ring

,

So when's the fast low noise photo diode amp coming out? How much? I've got lots of places to use more speed... but I'm very low volume.... sigh.

George H.

Bwuahahahaha! Said the guy that obviously doesn't know how the makers match up their lots.

The PH200 will be on the market soon. It's the fancy one, about 2 dB over shot noise, ca 1 MHz bw at nA photocurrents. Then we'll do a small/cheap/OEM version, a little noisier.

John

"George Hairoil the Retard "

Phil, I was just reading some other website, tolerance is the delta R at 25 C.

** Bullshit.

So the tempco is irrellevant.

** Bullshit.

.... Phil

g ,

The "PH200", I love it. I have dreams of turning our optical pumping apparatus into a magnetometer. It needs about a 3 MHz bandwidth with ~10 uA of photocurrent (onto a 0.25" diameter PD). Unfortunately this addition might be expected to sell an additional (1) optical pumping apparatus per year. (and that's on a good year.)

Then there are lots of fun things to do with a small low noise ~

100MHz photodiode.

Will the PH200 allow you to trade 'gain' for bandwidth?

George H.

Not currently.

We are considering doing an o/e converter with two electrical outputs, one the "normal" X1 gain, and a second hard-clipped X100 or X1000 gain. That would be for lidar-ish systems where a big transmit pulse would be followed by some weak echoes, or equivalent. The one we have in mind, for a laser application, would in fact be 100 MHz bw.

John

OK Phil, I give up. What should I know about tolerance?

What is the aging characteristics of those 10 Mohm resistors ?

If the good one are selected after manufacturing, will those components still be within 0.1 % after a few years in storage or after

10 years of use in actual equipment ?

"George Hairoil the Retard "

OK Phil, I give up. What should I know about tolerance?

** Either

1. Look it up using GOOGLE or

2. Post a question about it here for others to tell you.

It is absolutely BASIC stuff so maybe try SEB !!!

That you do not know already is APPALLING !!

That you refuse to control your monstrously bloated, autistic ego and admit to * yourself * that you need to find out is UTTERLY DISGUSTING !!!

.... Phil

Hey, speaking of tolerance, you might consider acquiring a little.

John

it

=A0!!!

it

=A0!!!

Opps ignore the previous post...

Sorry for the ego problem. (Most of the time I feel pretty ignorant when reading threads on SED.) I try to let people know when I'm guessing and when I 'think' I really know something.

Can anyone here help me figure out what crucial fact about resistor tolerance I am apparently unaware of? (I know this is a bit like trying to guess what color shirt Phil is wearing.... it would be nice if Phil would enlighten me... at least a hint.)

It's not to do with a bimodal distribution, nor the tempco. So perhaps the voltage rating, aging? Are there ever any non-linear terms...

I googled resistor tolerance.. but found nothing of much help on the first ten hit's.

George H.

As John said, the wringout is done, and once the datasheet is finished, one of us will post a link.

For anyone curious, the PH200 is a moderate-bandwidth transimpedance amp that uses what the marketing department calls a 'photon coupled transimpedance architecture'. That gets it more than an order of magnitude improvement in the noise vs bandwidth tradeoff compared to other commercial TIAs, and to any of my published ones. Here's a link to the datasheet plot of noise vs photocurrent, from data taken last week by yours truly:

It's shot noise limited above about 60 nA with a 1 MHz bandwidth, and its noise is asymptotically 1.76 dB above shot noise at higher photocurrents. (1.76 dB is 10*log(1.5), which gives a hint at how it works.)

You can get noise of that order with really small photodiodes, but this one is a nice big 7 sq mm (2.3 x 2.3 mm), so you can actually get your beam on there with no big problems, and don't have to worry about focusing a 20 nW beam!

The PH200 design has benefited greatly from collaboration with John and one of his engineers, Jonathan Dufour. More stuff Real Soon Now.

The series is intended to make it easier for people to do their actual scientific work, by taking as many as possible of the nasty practical problems and nailing them to the floor, so it's like they were never there. Stuff like TIA noise peaking, laser intensity noise, ground loops, mode hopping, and so on and so forth.

The motto of the series, coined by Rob Gaddi, an occasional SED contributor, is "Be Done, Now."

(The name is an ironic reference to Hewlett-Packard's first product, of course.)

Cheers

Phil Hobbs