Forums

Miniature solenoid

Started by Prof78 November 21, 2011
        Looking for a miniature (micro) latching solenoid mechanism to
effectively replace a latching reed relay used to introduce a
calibration current, e.g. 1femtoamp, into the input of a very high
gain
transimpedance amplifier (100Tohm) so that in normal operation the
'relay' is completely disconnected to avoid leakage. Stroke required
is
small (say ~2mm) and time response is not important. Linear (or
rotary)
motion solenoids from usual sources are rather larger than convenient
but hope somebody may know of source of a suitable mechanism, or maybe
one used in a commercial system.

Yours sincerely, Scott Hamilton.
On Mon, 21 Nov 2011 04:02:04 -0800 (PST), Prof78
<scott.hamilton@manchester.ac.uk> wrote:

> > Looking for a miniature (micro) latching solenoid mechanism to >effectively replace a latching reed relay used to introduce a >calibration current, e.g. 1femtoamp, into the input of a very high >gain >transimpedance amplifier (100Tohm) so that in normal operation the >'relay' is completely disconnected to avoid leakage. Stroke required >is >small (say ~2mm) and time response is not important. Linear (or >rotary) >motion solenoids from usual sources are rather larger than convenient >but hope somebody may know of source of a suitable mechanism, or maybe >one used in a commercial system. > >Yours sincerely, Scott Hamilton.
Where do you get the calibrated femtoamp from? How long do you need the calibration current to be on? I'm thinking a linear voltage ramp into a very small capacitor might work. It doesn't need an isolation switch. John
On Nov 21, 12:02=A0pm, Prof78 <scott.hamil...@manchester.ac.uk> wrote:

> =A0 =A0 =A0 =A0 Looking for a miniature (micro) latching solenoid mechani=
sm to
> effectively replace a latching reed relay used to introduce a > calibration current, e.g. 1femtoamp, into the input of a very high > gain > transimpedance amplifier (100Tohm) so that in normal operation the > 'relay' is completely disconnected to avoid leakage. Stroke required > is > small (say ~2mm) and time response is not important. Linear (or > rotary) > motion solenoids from usual sources are rather larger than convenient > but hope somebody may know of source of a suitable mechanism, or maybe > one used in a commercial system. > > Yours sincerely, Scott Hamilton.
cant you replace the existing reed? Or rewind the coil? Rapidonline do/ did a small bistable relay, and are in the UK. NT
"Prof78" <scott.hamilton@manchester.ac.uk> wrote in message
news:42894e2f-9f63-4e8d-b6b6-60dc732085f0@i6g2000vbe.googlegroups.com...
> > Looking for a miniature (micro) latching solenoid mechanism to > effectively replace a latching reed relay used to introduce a > calibration current, e.g. 1femtoamp, into the input of a very high > gain > transimpedance amplifier (100Tohm) so that in normal operation the > 'relay' is completely disconnected to avoid leakage. Stroke required > is > small (say ~2mm) and time response is not important. Linear (or > rotary) > motion solenoids from usual sources are rather larger than convenient > but hope somebody may know of source of a suitable mechanism, or maybe > one used in a commercial system. > > Yours sincerely, Scott Hamilton.
In the 80's I was using the Aromat S2E-L2 relays in my designs to measure fA currents. This is not a reed relay and it was a low thermal EMF type designed for uV applications but it worked a charm measuring opamp Ib too. Careful layout is critical, as is ES shielding of the fA circuitry on the PCB. If your need is one-off for lab use then you may want to look at the S2E-L2 as your solenoid. Stripping the case and attaching directly to the armature may get you what you need. Good luck. Art
On Nov 21, 4:13=A0pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Mon, 21 Nov 2011 04:02:04 -0800 (PST), Prof78 > > > > > > > > > > <scott.hamil...@manchester.ac.uk> wrote: > > > =A0 =A0 =A0 =A0Looking for a miniature (micro) latching solenoid mechan=
ism to
> >effectively replace a latching reed relay used to introduce a > >calibration current, e.g. 1femtoamp, into the input of a very high > >gain > >transimpedance amplifier (100Tohm) so that in normal operation the > >'relay' is completely disconnected to avoid leakage. Stroke required > >is > >small (say ~2mm) and time response is not important. Linear (or > >rotary) > >motion solenoids from usual sources are rather larger than convenient > >but hope somebody may know of source of a suitable mechanism, or maybe > >one used in a commercial system. > > >Yours sincerely, Scott Hamilton. > > Where do you get the calibrated femtoamp from? > > How long do you need the calibration current to be on? I'm thinking a > linear voltage ramp into a very small capacitor might work. It doesn't > need an isolation switch. > > John
In recent times the National/Calibration labs have realized the need for calibration at very low currents e.g. Willenberg G-D, Tauscher H N and Warnecke P 2003 A Traceable Precision Current Source for Currents Between 100aA and 10pA IEEE Trans. Instrum. Meas. 52, 436-9 (at P.T.Bundesanstalt, Braunschweig van den Brom H E, Court P de la, Rietveld G 2005 Accurate Subpicoampere Current Source Based on a Differentiating Capacitor With Software-Controlled Nonlinearity Compensation IEEE Trans. Instrum. Meas. 54, 554-8 though the technique goes back at least as far as: Praglin J, Nichols W A 1960 High-speed electrometers for rocket and satellite experiments Proc. I.R.E. 48, 771-9 and I have used a crude version of this so far, but knowing accurately the value of the capacitor presents considerable difficulty. For the present application there are five or more amplifiers ( they are operated in an evacuated and temperature controlled housing measuring ion currents in a mass spectrometer) and the need is to intercalibrate them so having a separate input capacitor on each is not feasible. Any connection present during normal amplifier operation can introduce noise and extra capacity affects the stability and frequency response. Retrofitting to existing spectrometers very much limits the space available. The operation also needs to be compatible with the existing control system. Scott.
On Nov 21, 4:02 am, Prof78 <scott.hamil...@manchester.ac.uk> wrote:
> Looking for a miniature (micro) latching solenoid mechanism to > effectively replace a latching reed relay used to introduce a > calibration current, e.g. 1femtoamp, into the input of a very high > gain > transimpedance amplifier (100Tohm) so that in normal operation the > 'relay' is completely disconnected to avoid leakage. Stroke required > is > small (say ~2mm) and time response is not important. Linear (or > rotary) > motion solenoids from usual sources are rather larger than convenient > but hope somebody may know of source of a suitable mechanism, or maybe > one used in a commercial system. > > Yours sincerely, Scott Hamilton.
I'm curious, would a mercury switch work, or would it have leakage when off? Ken
On Mon, 21 Nov 2011 04:02:04 -0800 (PST), Prof78
<scott.hamilton@manchester.ac.uk> wrote:

> > Looking for a miniature (micro) latching solenoid mechanism to >effectively replace a latching reed relay used to introduce a >calibration current, e.g. 1femtoamp, into the input of a very high >gain >transimpedance amplifier (100Tohm) so that in normal operation the >'relay' is completely disconnected to avoid leakage. Stroke required >is >small (say ~2mm) and time response is not important. Linear (or >rotary) >motion solenoids from usual sources are rather larger than convenient >but hope somebody may know of source of a suitable mechanism, or maybe >one used in a commercial system. > >Yours sincerely, Scott Hamilton.
I would use a to-99 latching relay, good ones are clean past sub-picoampere levels. Not sure where to get them these days, but they were plentiful 30 years ago. ?-)
On Tue, 22 Nov 2011 06:32:27 -0800 (PST), Prof78
<scott.hamilton@manchester.ac.uk> wrote:

>On Nov 21, 4:13&#2013266080;pm, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Mon, 21 Nov 2011 04:02:04 -0800 (PST), Prof78 >> >> >> >> >> >> >> >> >> >> <scott.hamil...@manchester.ac.uk> wrote: >> >> > &#2013266080; &#2013266080; &#2013266080; &#2013266080;Looking for a miniature (micro) latching solenoid mechanism to >> >effectively replace a latching reed relay used to introduce a >> >calibration current, e.g. 1femtoamp, into the input of a very high >> >gain >> >transimpedance amplifier (100Tohm) so that in normal operation the >> >'relay' is completely disconnected to avoid leakage. Stroke required >> >is >> >small (say ~2mm) and time response is not important. Linear (or >> >rotary) >> >motion solenoids from usual sources are rather larger than convenient >> >but hope somebody may know of source of a suitable mechanism, or maybe >> >one used in a commercial system. >> >> >Yours sincerely, Scott Hamilton. >> >> Where do you get the calibrated femtoamp from? >> >> How long do you need the calibration current to be on? I'm thinking a >> linear voltage ramp into a very small capacitor might work. It doesn't >> need an isolation switch. >> >> John > >In recent times the National/Calibration labs have realized the need >for calibration at very low currents e.g. >Willenberg G-D, Tauscher H N and Warnecke P 2003 A Traceable Precision >Current Source > for Currents Between 100aA and 10pA IEEE Trans. Instrum. Meas. 52, >436-9 (at > P.T.Bundesanstalt, Braunschweig >van den Brom H E, Court P de la, Rietveld G 2005 Accurate >Subpicoampere Current Source >Based on a Differentiating Capacitor With Software-Controlled >Nonlinearity Compensation IEEE Trans. Instrum. Meas. 54, 554-8 > >though the technique goes back at least as far as: > >Praglin J, Nichols W A 1960 High-speed electrometers for rocket and >satellite experiments >Proc. I.R.E. 48, 771-9 > >and I have used a crude version of this so far, but knowing accurately >the value of the capacitor presents considerable difficulty. For the >present application there are five or more amplifiers ( they are >operated in an evacuated and temperature controlled housing measuring >ion currents in a mass spectrometer) and the need is to intercalibrate >them so having a separate input capacitor on each is not feasible. >Any connection present during normal amplifier operation can introduce >noise and extra capacity affects the stability and frequency response. >Retrofitting to existing spectrometers very much limits the space >available. The operation also needs to be compatible with the existing >control system. > >Scott.
OK. What do you use to generate the cal current? A steerable electron beam would be interesting. John
On Nov 22, 4:12=A0pm, "Ken S. Tucker" <dynam...@vianet.on.ca> wrote:
> On Nov 21, 4:02 am, Prof78 <scott.hamil...@manchester.ac.uk> wrote: > > > =A0 =A0 =A0 =A0 Looking for a miniature (micro) latching solenoid mecha=
nism to
> > effectively replace a latching reed relay used to introduce a > > calibration current, e.g. 1femtoamp, into the input of a very high > > gain > > transimpedance amplifier (100Tohm) so that in normal operation the > > 'relay' is completely disconnected to avoid leakage. Stroke required > > is > > small (say ~2mm) and time response is not important. Linear (or > > rotary) > > motion solenoids from usual sources are rather larger than convenient > > but hope somebody may know of source of a suitable mechanism, or maybe > > one used in a commercial system. > > I'm curious, would a mercury switch work, or would it have leakage > when off?
Mercury-wetted reeds have no more leakage than any other reed relay. If you apply enough volts you can get some leakage through the glass from ion migration - the electro-luminescence from this limited the voltage we could put across a photomultiplier-tube face-plate in the Everhart-Thornley detector on the Cambridge Instruments electron microscopes to less than one thousand volts. http://en.wikipedia.org/wiki/Everhart-Thornley_detector -- Bill Sloman, Nijmegen
On 22/11/2011 14:32, Prof78 wrote:

> and I have used a crude version of this so far, but knowing accurately > the value of the capacitor presents considerable difficulty. For the > present application there are five or more amplifiers ( they are > operated in an evacuated and temperature controlled housing measuring > ion currents in a mass spectrometer) and the need is to intercalibrate > them so having a separate input capacitor on each is not feasible. > Any connection present during normal amplifier operation can introduce > noise and extra capacity affects the stability and frequency response. > Retrofitting to existing spectrometers very much limits the space > available. The operation also needs to be compatible with the existing > control system.
Aren't you also going to have some fun and games to avoid infringing the various patents on the reference current calibration systems - or have they just expired recently? Or is it a one off at a uni? We typically used a very stable reference voltage, a 10^11 ohm resistor and a bunch of carefully selected reed relays. Timing was critical to get the optimum solution same applies for systematic zero offsets. The kit chosen usually has to be able to survive being hot baked to get a hard vacuum too which is a minor detail you seem to have omitted to mention. I assume here you are talking about a gain and offset reference system for a multicollector Thermal Ionisation MassSpec. -- Regards, Martin Brown