On Tue, 17 Apr 2012 19:13:53 -0700, "Mr.CRC"
<crobcBOGUS@REMOVETHISsbcglobal.net> wrote:
>
>>>> Teflon is not a good idea, due to microphonics.
>>> Depends on how much signal he has. I'd expect an engine explosion to
>>> make lots of signal.
>>=20
>> That also depends on how much gets to the sensor crystal. It can't =
take
>> direct exposure to the combustion chamber gasses, for heat and =
chemical
>> issues. Thus attenuation, maybe a lot of it, before the sensor =
crystal
>> "sees" it.
>
>
>Our engine in-cylinder pressure sensors are flush with the head, so see
>the combustion chamber environment directly. I think all they have is a
>thin metal foil over the sensor material surface.
>
We may never know unless someone sections one.
?-)
Reply by Mr.CRC●April 17, 20122012-04-17
josephkk wrote:
> On Sun, 15 Apr 2012 14:58:31 -0700, John Larkin
> <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>
>> On Sun, 15 Apr 2012 23:15:07 +0300, Tauno Voipio
>> <tauno.voipio@notused.fi.invalid> wrote:
>>
>>> On 15.4.12 8:05 , John Larkin wrote:
>>>> On Sun, 15 Apr 2012 08:10:23 -0700, josephkk
>>>> <joseph_barrett@sbcglobal.net> wrote:
>>>>
>>>>> On Fri, 13 Apr 2012 07:19:40 -0700 (PDT), Geoffrey
>>>>> <gmortimer2003@yahoo.com> wrote:
>>>>>
>>>>>> On Apr 11, 2:49 am, josephkk<joseph_barr...@sbcglobal.net> wrote:
>>>>>>> On Tue, 3 Apr 2012 07:53:52 -0700 (PDT), Geoffrey
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> <gmortimer2...@yahoo.com> wrote:
>>>>>>>> Hi there
>>>>>>>> I have a charge amplifier, used to amplify the signal from a piezo
>>>>>>>> electric transducer, with 2nF of reference capacitance shunted with
>>>>>>>> 1GOhm. I need to be able to reset the amplifier, preferably with a
>>>>>>>> solid state device (the circuit has to be very compact, and operate in
>>>>>>>> a high-vibration environment). One possibility which comes to mind is
>>>>>>>> to simultaneously short the amplifier output and input to ground. The
>>>>>>>> input is the inverting input of the amplifier, and is nominally at the
>>>>>>>> same ground potential as the non inverting input. I am considering the
>>>>>>>> use of a mosfet as the shorting switch for the input. When the mosfet
>>>>>>>> is off, its gate will be at ground potential, as will its drain
>>>>>>>> (virtual ground) and source. Is there a mechanism whereby a leakage
>>>>>>>> current could still flow from drain to source? Every nanoampere of IDS
>>>>>>>> gives 1V of offset at the output, and it should be noted that the
>>>>>>>> circuit must work at 120 deg C.
>>>>>>>> Any help appreciated.
>>>>>>>> Best regards
>>>>>>>> Geoff
>>>>>>> As a test engineer at an earlier time i am troubled by the conditions you
>>>>>>> are subjecting your charge amplifier to. What constraints do you have
>>>>>>> that you cannot put your charge amplifier in a benign location, away from
>>>>>>> the heat and vibration?
>>>>>>>
>>>>>>> ?-)- Hide quoted text -
>>>>>>>
>>>>>>> - Show quoted text -
>>>>>> The amplifier will be placed in the Vee of a motor racing engine, the
>>>>>> piezo sensor being used to measure the pressure in the combustion
>>>>>> chamber. It is possible that a solution involving longer cables could
>>>>>> be found, but there are high levels of EMI due to ignition systems and
>>>>>> other power electronics. The temperature is a bit of a bother - few
>>>>>> charge amps are specified at 125 degrees due to the high leakage and
>>>>>> bias currents at that temperature.
>>>>> I was wondering. There is no need to subject the charge amplifier to that
>>>>> environment. It belongs in the driver compartment. Far less heat, and a
>>>>> bit less vibration. Of course you are paying about US$18/ft for the
>>>>> special shielded cable for either placement. (Shake and bake
>>>>> piezoelectric accelerometer cable from Endevco[, and perhaps Ling or
>>>>> Umhholz-Dickie].)
>>>>>
>>>>> ?-)
>>>> What's special about piezo cable? Any teflon coax, or semi-hardline
>>>> for super shielding, would work. He'll probably have lots of signal.
>>>>
>>>>
>>> Teflon is not a good idea, due to microphonics.
>> Depends on how much signal he has. I'd expect an engine explosion to
>> make lots of signal.
>
> That also depends on how much gets to the sensor crystal. It can't take
> direct exposure to the combustion chamber gasses, for heat and chemical
> issues. Thus attenuation, maybe a lot of it, before the sensor crystal
> "sees" it.
Our engine in-cylinder pressure sensors are flush with the head, so see
the combustion chamber environment directly. I think all they have is a
thin metal foil over the sensor material surface.
--
_____________________
Mr.CRC
crobcBOGUS@REMOVETHISsbcglobal.net
SuSE 10.3 Linux 2.6.22.17
Reply by josephkk●April 16, 20122012-04-16
On Sun, 15 Apr 2012 14:58:31 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
>On Sun, 15 Apr 2012 23:15:07 +0300, Tauno Voipio
><tauno.voipio@notused.fi.invalid> wrote:
>
>>On 15.4.12 8:05 , John Larkin wrote:
>>> On Sun, 15 Apr 2012 08:10:23 -0700, josephkk
>>> <joseph_barrett@sbcglobal.net> wrote:
>>>
>>>> On Fri, 13 Apr 2012 07:19:40 -0700 (PDT), Geoffrey
>>>> <gmortimer2003@yahoo.com> wrote:
>>>>
>>>>> On Apr 11, 2:49 am, josephkk<joseph_barr...@sbcglobal.net> wrote:
>>>>>> On Tue, 3 Apr 2012 07:53:52 -0700 (PDT), Geoffrey
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> <gmortimer2...@yahoo.com> wrote:
>>>>>>> Hi there
>>>>>>
>>>>>>> I have a charge amplifier, used to amplify the signal from a =
piezo
>>>>>>> electric transducer, with 2nF of reference capacitance shunted =
with
>>>>>>> 1GOhm. I need to be able to reset the amplifier, preferably with =
a
>>>>>>> solid state device (the circuit has to be very compact, and =
operate in
>>>>>>> a high-vibration environment). One possibility which comes to =
mind is
>>>>>>> to simultaneously short the amplifier output and input to ground.=
The
>>>>>>> input is the inverting input of the amplifier, and is nominally =
at the
>>>>>>> same ground potential as the non inverting input. I am =
considering the
>>>>>>> use of a mosfet as the shorting switch for the input. When the =
mosfet
>>>>>>> is off, its gate will be at ground potential, as will its drain
>>>>>>> (virtual ground) and source. Is there a mechanism whereby a =
leakage
>>>>>>> current could still flow from drain to source? Every nanoampere =
of IDS
>>>>>>> gives 1V of offset at the output, and it should be noted that the
>>>>>>> circuit must work at 120 deg C.
>>>>>>
>>>>>>> Any help appreciated.
>>>>>>
>>>>>>> Best regards
>>>>>>> Geoff
>>>>>>
>>>>>> As a test engineer at an earlier time i am troubled by the =
conditions you
>>>>>> are subjecting your charge amplifier to. What constraints do you =
have
>>>>>> that you cannot put your charge amplifier in a benign location, =
away from
>>>>>> the heat and vibration?
>>>>>>
>>>>>> ?-)- Hide quoted text -
>>>>>>
>>>>>> - Show quoted text -
>>>>>
>>>>> The amplifier will be placed in the Vee of a motor racing engine, =
the
>>>>> piezo sensor being used to measure the pressure in the combustion
>>>>> chamber. It is possible that a solution involving longer cables =
could
>>>>> be found, but there are high levels of EMI due to ignition systems =
and
>>>>> other power electronics. The temperature is a bit of a bother - few
>>>>> charge amps are specified at 125 degrees due to the high leakage =
and
>>>>> bias currents at that temperature.
>>>>
>>>> I was wondering. There is no need to subject the charge amplifier =
to that
>>>> environment. It belongs in the driver compartment. Far less heat, =
and a
>>>> bit less vibration. Of course you are paying about US$18/ft for the
>>>> special shielded cable for either placement. (Shake and bake
>>>> piezoelectric accelerometer cable from Endevco[, and perhaps Ling or
>>>> Umhholz-Dickie].)
>>>>
>>>> ?-)
>>>
>>> What's special about piezo cable? Any teflon coax, or semi-hardline
>>> for super shielding, would work. He'll probably have lots of signal.
>>>
>>>
>>
>>Teflon is not a good idea, due to microphonics.
>
>Depends on how much signal he has. I'd expect an engine explosion to
>make lots of signal.
That also depends on how much gets to the sensor crystal. It can't take
direct exposure to the combustion chamber gasses, for heat and chemical
issues. Thus attenuation, maybe a lot of it, before the sensor crystal
"sees" it.
?-)
Reply by John Larkin●April 15, 20122012-04-15
On Sun, 15 Apr 2012 23:15:07 +0300, Tauno Voipio
<tauno.voipio@notused.fi.invalid> wrote:
>On 15.4.12 8:05 , John Larkin wrote:
>> On Sun, 15 Apr 2012 08:10:23 -0700, josephkk
>> <joseph_barrett@sbcglobal.net> wrote:
>>
>>> On Fri, 13 Apr 2012 07:19:40 -0700 (PDT), Geoffrey
>>> <gmortimer2003@yahoo.com> wrote:
>>>
>>>> On Apr 11, 2:49 am, josephkk<joseph_barr...@sbcglobal.net> wrote:
>>>>> On Tue, 3 Apr 2012 07:53:52 -0700 (PDT), Geoffrey
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> <gmortimer2...@yahoo.com> wrote:
>>>>>> Hi there
>>>>>
>>>>>> I have a charge amplifier, used to amplify the signal from a piezo
>>>>>> electric transducer, with 2nF of reference capacitance shunted with
>>>>>> 1GOhm. I need to be able to reset the amplifier, preferably with a
>>>>>> solid state device (the circuit has to be very compact, and operate in
>>>>>> a high-vibration environment). One possibility which comes to mind is
>>>>>> to simultaneously short the amplifier output and input to ground. The
>>>>>> input is the inverting input of the amplifier, and is nominally at the
>>>>>> same ground potential as the non inverting input. I am considering the
>>>>>> use of a mosfet as the shorting switch for the input. When the mosfet
>>>>>> is off, its gate will be at ground potential, as will its drain
>>>>>> (virtual ground) and source. Is there a mechanism whereby a leakage
>>>>>> current could still flow from drain to source? Every nanoampere of IDS
>>>>>> gives 1V of offset at the output, and it should be noted that the
>>>>>> circuit must work at 120 deg C.
>>>>>
>>>>>> Any help appreciated.
>>>>>
>>>>>> Best regards
>>>>>> Geoff
>>>>>
>>>>> As a test engineer at an earlier time i am troubled by the conditions you
>>>>> are subjecting your charge amplifier to. What constraints do you have
>>>>> that you cannot put your charge amplifier in a benign location, away from
>>>>> the heat and vibration?
>>>>>
>>>>> ?-)- Hide quoted text -
>>>>>
>>>>> - Show quoted text -
>>>>
>>>> The amplifier will be placed in the Vee of a motor racing engine, the
>>>> piezo sensor being used to measure the pressure in the combustion
>>>> chamber. It is possible that a solution involving longer cables could
>>>> be found, but there are high levels of EMI due to ignition systems and
>>>> other power electronics. The temperature is a bit of a bother - few
>>>> charge amps are specified at 125 degrees due to the high leakage and
>>>> bias currents at that temperature.
>>>
>>> I was wondering. There is no need to subject the charge amplifier to that
>>> environment. It belongs in the driver compartment. Far less heat, and a
>>> bit less vibration. Of course you are paying about US$18/ft for the
>>> special shielded cable for either placement. (Shake and bake
>>> piezoelectric accelerometer cable from Endevco[, and perhaps Ling or
>>> Umhholz-Dickie].)
>>>
>>> ?-)
>>
>> What's special about piezo cable? Any teflon coax, or semi-hardline
>> for super shielding, would work. He'll probably have lots of signal.
>>
>>
>
>Teflon is not a good idea, due to microphonics.
Depends on how much signal he has. I'd expect an engine explosion to
make lots of signal.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Reply by Tauno Voipio●April 15, 20122012-04-15
On 15.4.12 8:05 , John Larkin wrote:
> On Sun, 15 Apr 2012 08:10:23 -0700, josephkk
> <joseph_barrett@sbcglobal.net> wrote:
>
>> On Fri, 13 Apr 2012 07:19:40 -0700 (PDT), Geoffrey
>> <gmortimer2003@yahoo.com> wrote:
>>
>>> On Apr 11, 2:49 am, josephkk<joseph_barr...@sbcglobal.net> wrote:
>>>> On Tue, 3 Apr 2012 07:53:52 -0700 (PDT), Geoffrey
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> <gmortimer2...@yahoo.com> wrote:
>>>>> Hi there
>>>>
>>>>> I have a charge amplifier, used to amplify the signal from a piezo
>>>>> electric transducer, with 2nF of reference capacitance shunted with
>>>>> 1GOhm. I need to be able to reset the amplifier, preferably with a
>>>>> solid state device (the circuit has to be very compact, and operate in
>>>>> a high-vibration environment). One possibility which comes to mind is
>>>>> to simultaneously short the amplifier output and input to ground. The
>>>>> input is the inverting input of the amplifier, and is nominally at the
>>>>> same ground potential as the non inverting input. I am considering the
>>>>> use of a mosfet as the shorting switch for the input. When the mosfet
>>>>> is off, its gate will be at ground potential, as will its drain
>>>>> (virtual ground) and source. Is there a mechanism whereby a leakage
>>>>> current could still flow from drain to source? Every nanoampere of IDS
>>>>> gives 1V of offset at the output, and it should be noted that the
>>>>> circuit must work at 120 deg C.
>>>>
>>>>> Any help appreciated.
>>>>
>>>>> Best regards
>>>>> Geoff
>>>>
>>>> As a test engineer at an earlier time i am troubled by the conditions you
>>>> are subjecting your charge amplifier to. What constraints do you have
>>>> that you cannot put your charge amplifier in a benign location, away from
>>>> the heat and vibration?
>>>>
>>>> ?-)- Hide quoted text -
>>>>
>>>> - Show quoted text -
>>>
>>> The amplifier will be placed in the Vee of a motor racing engine, the
>>> piezo sensor being used to measure the pressure in the combustion
>>> chamber. It is possible that a solution involving longer cables could
>>> be found, but there are high levels of EMI due to ignition systems and
>>> other power electronics. The temperature is a bit of a bother - few
>>> charge amps are specified at 125 degrees due to the high leakage and
>>> bias currents at that temperature.
>>
>> I was wondering. There is no need to subject the charge amplifier to that
>> environment. It belongs in the driver compartment. Far less heat, and a
>> bit less vibration. Of course you are paying about US$18/ft for the
>> special shielded cable for either placement. (Shake and bake
>> piezoelectric accelerometer cable from Endevco[, and perhaps Ling or
>> Umhholz-Dickie].)
>>
>> ?-)
>
> What's special about piezo cable? Any teflon coax, or semi-hardline
> for super shielding, would work. He'll probably have lots of signal.
>
>
Teflon is not a good idea, due to microphonics.
Reply by John Larkin●April 15, 20122012-04-15
On Sun, 15 Apr 2012 08:10:23 -0700, josephkk
<joseph_barrett@sbcglobal.net> wrote:
>On Fri, 13 Apr 2012 07:19:40 -0700 (PDT), Geoffrey
><gmortimer2003@yahoo.com> wrote:
>
>>On Apr 11, 2:49�am, josephkk <joseph_barr...@sbcglobal.net> wrote:
>>> On Tue, 3 Apr 2012 07:53:52 -0700 (PDT), Geoffrey
>>>
>>>
>>>
>>>
>>>
>>> <gmortimer2...@yahoo.com> wrote:
>>> >Hi there
>>>
>>> >I have a charge amplifier, used to amplify the signal from a piezo
>>> >electric transducer, with 2nF of reference capacitance shunted with
>>> >1GOhm. I need to be able to reset the amplifier, preferably with a
>>> >solid state device (the circuit has to be very compact, and operate in
>>> >a high-vibration environment). One possibility which comes to mind is
>>> >to simultaneously short the amplifier output and input to ground. The
>>> >input is the inverting input of the amplifier, and is nominally at the
>>> >same ground potential as the non inverting input. I am considering the
>>> >use of a mosfet as the shorting switch for the input. When the mosfet
>>> >is off, its gate will be at ground potential, as will its drain
>>> >(virtual ground) and source. Is there a mechanism whereby a leakage
>>> >current could still flow from drain to source? Every nanoampere of IDS
>>> >gives 1V of offset at the output, and it should be noted that the
>>> >circuit must work at 120 deg C.
>>>
>>> >Any help appreciated.
>>>
>>> >Best regards
>>> >Geoff
>>>
>>> As a test engineer at an earlier time i am troubled by the conditions you
>>> are subjecting your charge amplifier to. �What constraints do you have
>>> that you cannot put your charge amplifier in a benign location, away from
>>> the heat and vibration?
>>>
>>> ?-)- Hide quoted text -
>>>
>>> - Show quoted text -
>>
>>The amplifier will be placed in the Vee of a motor racing engine, the
>>piezo sensor being used to measure the pressure in the combustion
>>chamber. It is possible that a solution involving longer cables could
>>be found, but there are high levels of EMI due to ignition systems and
>>other power electronics. The temperature is a bit of a bother - few
>>charge amps are specified at 125 degrees due to the high leakage and
>>bias currents at that temperature.
>
>I was wondering. There is no need to subject the charge amplifier to that
>environment. It belongs in the driver compartment. Far less heat, and a
>bit less vibration. Of course you are paying about US$18/ft for the
>special shielded cable for either placement. (Shake and bake
>piezoelectric accelerometer cable from Endevco[, and perhaps Ling or
>Umhholz-Dickie].)
>
>?-)
What's special about piezo cable? Any teflon coax, or semi-hardline
for super shielding, would work. He'll probably have lots of signal.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
>On Apr 11, 2:49=A0am, josephkk <joseph_barr...@sbcglobal.net> wrote:
>> On Tue, 3 Apr 2012 07:53:52 -0700 (PDT), Geoffrey
>>
>>
>>
>>
>>
>> <gmortimer2...@yahoo.com> wrote:
>> >Hi there
>>
>> >I have a charge amplifier, used to amplify the signal from a piezo
>> >electric transducer, with 2nF of reference capacitance shunted with
>> >1GOhm. I need to be able to reset the amplifier, preferably with a
>> >solid state device (the circuit has to be very compact, and operate =
in
>> >a high-vibration environment). One possibility which comes to mind is
>> >to simultaneously short the amplifier output and input to ground. The
>> >input is the inverting input of the amplifier, and is nominally at =
the
>> >same ground potential as the non inverting input. I am considering =
the
>> >use of a mosfet as the shorting switch for the input. When the mosfet
>> >is off, its gate will be at ground potential, as will its drain
>> >(virtual ground) and source. Is there a mechanism whereby a leakage
>> >current could still flow from drain to source? Every nanoampere of =
IDS
>> >gives 1V of offset at the output, and it should be noted that the
>> >circuit must work at 120 deg C.
>>
>> >Any help appreciated.
>>
>> >Best regards
>> >Geoff
>>
>> As a test engineer at an earlier time i am troubled by the conditions =
you
>> are subjecting your charge amplifier to. =A0What constraints do you =
have
>> that you cannot put your charge amplifier in a benign location, away =
from
>> the heat and vibration?
>>
>> ?-)- Hide quoted text -
>>
>> - Show quoted text -
>
>The amplifier will be placed in the Vee of a motor racing engine, the
>piezo sensor being used to measure the pressure in the combustion
>chamber. It is possible that a solution involving longer cables could
>be found, but there are high levels of EMI due to ignition systems and
>other power electronics. The temperature is a bit of a bother - few
>charge amps are specified at 125 degrees due to the high leakage and
>bias currents at that temperature.
I was wondering. There is no need to subject the charge amplifier to =
that
environment. It belongs in the driver compartment. Far less heat, and a
bit less vibration. Of course you are paying about US$18/ft for the
special shielded cable for either placement. (Shake and bake
piezoelectric accelerometer cable from Endevco[, and perhaps Ling or
Umhholz-Dickie].)
?-)
>On Apr 11, 2:49�am, josephkk <joseph_barr...@sbcglobal.net> wrote:
>> On Tue, 3 Apr 2012 07:53:52 -0700 (PDT), Geoffrey
>>
>>
>>
>>
>>
>> <gmortimer2...@yahoo.com> wrote:
>> >Hi there
>>
>> >I have a charge amplifier, used to amplify the signal from a piezo
>> >electric transducer, with 2nF of reference capacitance shunted with
>> >1GOhm. I need to be able to reset the amplifier, preferably with a
>> >solid state device (the circuit has to be very compact, and operate in
>> >a high-vibration environment). One possibility which comes to mind is
>> >to simultaneously short the amplifier output and input to ground. The
>> >input is the inverting input of the amplifier, and is nominally at the
>> >same ground potential as the non inverting input. I am considering the
>> >use of a mosfet as the shorting switch for the input. When the mosfet
>> >is off, its gate will be at ground potential, as will its drain
>> >(virtual ground) and source. Is there a mechanism whereby a leakage
>> >current could still flow from drain to source? Every nanoampere of IDS
>> >gives 1V of offset at the output, and it should be noted that the
>> >circuit must work at 120 deg C.
>>
>> >Any help appreciated.
>>
>> >Best regards
>> >Geoff
>>
>> As a test engineer at an earlier time i am troubled by the conditions you
>> are subjecting your charge amplifier to. �What constraints do you have
>> that you cannot put your charge amplifier in a benign location, away from
>> the heat and vibration?
>>
>> ?-)- Hide quoted text -
>>
>> - Show quoted text -
>
>The amplifier will be placed in the Vee of a motor racing engine, the
>piezo sensor being used to measure the pressure in the combustion
>chamber. It is possible that a solution involving longer cables could
>be found, but there are high levels of EMI due to ignition systems and
>other power electronics. The temperature is a bit of a bother - few
>charge amps are specified at 125 degrees due to the high leakage and
>bias currents at that temperature.
I should think that you'd get a huge signal from that setup. Why not
run well-shielded coax to a remote charge amp in a friendlier
location?
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Reply by Geoffrey●April 13, 20122012-04-13
On Apr 11, 2:49=A0am, josephkk <joseph_barr...@sbcglobal.net> wrote:
> On Tue, 3 Apr 2012 07:53:52 -0700 (PDT), Geoffrey
>
>
>
>
>
> <gmortimer2...@yahoo.com> wrote:
> >Hi there
>
> >I have a charge amplifier, used to amplify the signal from a piezo
> >electric transducer, with 2nF of reference capacitance shunted with
> >1GOhm. I need to be able to reset the amplifier, preferably with a
> >solid state device (the circuit has to be very compact, and operate in
> >a high-vibration environment). One possibility which comes to mind is
> >to simultaneously short the amplifier output and input to ground. The
> >input is the inverting input of the amplifier, and is nominally at the
> >same ground potential as the non inverting input. I am considering the
> >use of a mosfet as the shorting switch for the input. When the mosfet
> >is off, its gate will be at ground potential, as will its drain
> >(virtual ground) and source. Is there a mechanism whereby a leakage
> >current could still flow from drain to source? Every nanoampere of IDS
> >gives 1V of offset at the output, and it should be noted that the
> >circuit must work at 120 deg C.
>
> >Any help appreciated.
>
> >Best regards
> >Geoff
>
> As a test engineer at an earlier time i am troubled by the conditions you
> are subjecting your charge amplifier to. =A0What constraints do you have
> that you cannot put your charge amplifier in a benign location, away from
> the heat and vibration?
>
> ?-)- Hide quoted text -
>
> - Show quoted text -
The amplifier will be placed in the Vee of a motor racing engine, the
piezo sensor being used to measure the pressure in the combustion
chamber. It is possible that a solution involving longer cables could
be found, but there are high levels of EMI due to ignition systems and
other power electronics. The temperature is a bit of a bother - few
charge amps are specified at 125 degrees due to the high leakage and
bias currents at that temperature.
>Hi there
>
>I have a charge amplifier, used to amplify the signal from a piezo
>electric transducer, with 2nF of reference capacitance shunted with
>1GOhm. I need to be able to reset the amplifier, preferably with a
>solid state device (the circuit has to be very compact, and operate in
>a high-vibration environment). One possibility which comes to mind is
>to simultaneously short the amplifier output and input to ground. The
>input is the inverting input of the amplifier, and is nominally at the
>same ground potential as the non inverting input. I am considering the
>use of a mosfet as the shorting switch for the input. When the mosfet
>is off, its gate will be at ground potential, as will its drain
>(virtual ground) and source. Is there a mechanism whereby a leakage
>current could still flow from drain to source? Every nanoampere of IDS
>gives 1V of offset at the output, and it should be noted that the
>circuit must work at 120 deg C.
>
>Any help appreciated.
>
>Best regards
>Geoff
As a test engineer at an earlier time i am troubled by the conditions you
are subjecting your charge amplifier to. What constraints do you have
that you cannot put your charge amplifier in a benign location, away from
the heat and vibration?
?-)