The connector is an SO-239 (female), often called a UHF connector. Its mate is a PL-259 (male). They are very common and most often used for HF applications. For this a;application, the connectors need to use Teflon for the insulation and they are a bit rare.
It isn't hard for low current; just a low-leakage capacitor and a slow ramp generator, and you have a low-current reference. Some way to discharge the capacitor (clipleads and teflon turret terminals?) is needed.
Teflon and some ceramics are the best capacitor types; 100 pF gives you Iout = (1e-10) dV/dt and I've made ramp generators that did about 10 mv/hour, and can keep it up all day. that'd be Iout in the 3e-16 amps range...
You calibrate the ramp generator with a DVM and stopwatch.
HP 3325As make nice ramps down to 1 uHz, and they're nearly as cheap as 610 Cs. It's not a modern DDS/arb architecture, so I don't think its output is a staircase.
Cheers
Phil Hobbs
You could charge a 10 uF cap through a 1G resistor, and couple that into a picoammeter through a 10 pF cap. 10 volts makes 10 nA which becomes 10 fA.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Ceramic caps that big are pretty nonlinear to use for calibration, no? I have some 2-uf 200V dogbone mylars. When my 610C gets here this evening I'll test their insulation resistance. ;)
An LM662 triangle wave generator with one of your patented bootstrapped-voltage-references could go pretty slowly.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
A 10 pF NPO should be pretty good on the output side. I'd use a film cap for the big one.
Yeah, if you want a linear ramp a bootstrap current source is a good way to go, almost the only way to go if you want, say, 1 nA.
Film cap, cmos opamp follower, bandgap level shifter, 1G resistor back to the cap. Reset it with a paper clip.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
The $125 610C arrived just now, by UPS ground all the way from SoCal. At first blush, it looks like it works pretty well. It zeroes fine, which is one of the main indications of health. No trace of stickiness in the meter movement, which is another important indication.
On the 10 fA FS range, with the input disconnected but with the cap off the connector, waving my hand a foot away from the front panel makes the meter move all over the place.
Works on both the slow and fast settings.
Very pretty!
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Resistance reads about 2% low up to 1E12 ohms, calibrated using a 5-1/2 digit, 10M DVM and a 10V HP precision power supply. A Russian 1 teraohm
10% resistor reads about 0.86 Tohms on the 610C and about 0.89 Tohms using the digital voltmeter trick. The fast setting pegs the meter in the resistance mode. (I didn't try re-zeroing it.)Voltage is within 1% where I looked.
Stability is excellent--on the 10 fA FS range, it stays zeroed to within
1% of FS over several minutes, and that's after only about half an hour of warm-up.With a 100 pF polystyrene cap across the input (just so I know roughly what the capacitance is there), and measuring the 0-3V output on the back near full scale (2.986V), the voltage decay is less than 100 uV/min and is consistent with zero.
That means the input current on the 10V range is less than
100uV * 10V/3V * 100 pF /60 s = 0.5 fA. Amazing. (Not bad on the polystyrene, either.)I measured a 2.2 uF 600V wound mylar, charged to 10V for a few seconds. On the 10-V range, it produced nearly full scale on the 0-3V DC output. This output dropped about 220uV out of 3V in 3 minutes, for a self-discharge time constant of about 2.4 million seconds (about a month). So with a 47 G resistor and an LM662, you could actually make a decent 10 microhertz sawtooth out of it.
Not a bad gizmo for $125 plus $25 shipping!
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
It's a beautiful instrument, as long as you don't look inside. It's sort of a rat's nest.
The change you are seeing on the mylar cap may be dielectric absorption, maybe not leakage. They are awful that way.
Someone here once posted a long-term measurement of film cap leakage, and as I recall he saw essentially zero voltage change per year for some.
Interestingly the major source of instability on the 10 fA range appears to be slow capacitive pickup from things moving around inside as it warms up. You can make it move > 10 fA in each direction by pressing gently on the front panel. Pushing on the range switch knob is about
10x more sensitive.When you're down in the hundreds of electrons, these things matter!
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
1 fA is 6000 of them per second.
Hey, back to the flame detector. What does a typical flame sound like? On o/e converter and some headphones might be interesting. Burning cotton must have features.
Imagine listening to a fireworks display, or a sparkler, or a gunshot, or a fountain. Lightning.
When I was a kid, I used to walk around listening to magnetic fields and electric fields and light. I was a weird kid.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Yup. The meter is a bit faster than that, of course, and the fluctuations are smaller than 1/10 of full scale (fun).
Diffusion flames such as candles and small sparks are pretty quiet, I expect. Certainly quiet compared with all the vibrating duct work and reciprocating machinery and cussing workers. ;)
When did that end?
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
I assume you're keeping yourself ground during these proddings, (I grab the front panel ground... what did you grab?) Isn't there some bootstrap/feedback thing to get rid of the input C? That will depend the panel shape... and input knobs/switches are sensitive to pickup.
(I just shipped this one/ two/ few of circuit in a plastic box. I had to put a ground strapped lug onto a toggle switch. Else when you touched it, you got 10's mV into 100 k ohm. well that's the pickup in my lab.) (Almost all my circuits suffer the cardinal sin of running the signal through control panel pots and switches... I tuck all the active elements right next to the switches/ pots, and that's worked so far. :^)
George H.
This was done with the metal blank cap across the input jack (a Keithley special teflon SO-239). With the cap in place, it makes no difference if I ground myself to the chassis or not.
Interestingly, with the cap off, if I grab hold of the connector body (ground) I can still make the meter move a whole lot by flexing my fingers.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Electric fields and magnetic fields and light. I think that's how we all here make money? (Well except for the dang thermal thing. and of course mechanicals to hold it together...)
Aside but 610 related The newark guy stopped by earlier in the week with another sample of the leaky mill max part. I hooked it up and it looks less leaky....(sigh) I didn't have time to do comparison testing. But I feel like the plastic mix is changing.
I've got a circuit where I have to have a socket, Which means I have to test each batch... what if it ages over time? (I would have thought someone had already figured out the best plastic for sockets?) Bare single sockets are looking very appealing. They are easy to replace if you can solder!
George H.
Being a kid, or being weird? Neither.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
I'm relieved to hear that. Thought I might have missed something ultra-important.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Mine's pretty steady at 1 pF full scale. The most sensitive current range, 1e-14 amps full scale, looks useless. It drifts like crazy and tiny mechanical forces on the case move it several fA.
My homebrew meter had a similar background drift, 5 fA ballpark. It would take some serious work to measure a few fA with any sort of accuracy.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
--- Lack of beauty is in the eye of the beholder, and if one can't appreciate the underpinning of the builder's reasons for constructing its nest in a certain way doesn't detract from its beauty.
---
--- "may be" and "maybe not" sound like ignorance in that dielectric absorbtion results in an increase in voltage across the capacitor's terminals once it's been discharged, while leakage results in the lowering of voltage across the capacitor's terminals due to electron migration through its dielectric.
---
--- A link corroberating your opinion would be nice, since your opinion is somewhat suspect.
John Fields
You should "be a kid" for as much time as you can afford. For me being a kid is playing around with circuits and instruments... all that good stuff.
Not to be too much of a downer, but my poor mum with alzheimer's is turning into a kid, which totally sucks.
sorry, George H.
My poor mum, is turning into a kid too. Which pretty much sucks, (sorry for any downer.)
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