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Tek 576 Curve Tracer solid state replacement for relays ?


garp66
 

hi,
Wondering if anyone has replaced any of the mechanical relays in a Tek 576 ( Or any to the other curve tracers) , with solid state relays ?

There might be some issue with HV areas, but modern HV IR HexFets might be able to handle the HV.

rick


Brad Thompson
 

garp66 wrote on 1/6/2020 5:01 PM:

hi,
Wondering if anyone has replaced any of the mechanical relays in a Tek 576 ( Or any to the other curve tracers) , with solid state relays ?

There might be some issue with HV areas, but modern HV IR HexFets might be able to handle the HV.

rick
Hello--

A solid-state relay (SSR) uses a semiconductor device as the electrical contact.
The voltage drop across the device varies with the contact current and
hence could introduce an error. A clunky old mechanical contact is
better in this respect.

If you were starting a curve-tracer design, you could investigate  SSR properties
and possibly compensate for errors, but retrofitting SSRs in an existing
curve tracer would be messy,

73--

Brad  AA1IP


garp66
 

hi

Still I wonder if *any* of the Tek 576 relays could be replaced with power Mosfets.
I am curious if some Hexfet / Mosfet relay replacement(s) might then be more reliable ?

Brad:
Are all of the relays in the Tek 576 that you are referring to susceptible to the issue you have brought up ?

I have used a number of different power Hexfets , Mosfets made by IR ( IRF.com ) , having very low "On" resistances ( 0.0001 Ohms ) at various voltages. These Fets are capable of being turned 'on' via the output of a single TTL gate, without issue. I have also placed these in series or parallel (D-S) to achieve a wider ranges of specification with good results.

rick


garp66
 

Sorry, typo correction: Not 0.0001 Ohm

RDS of 0.001Ohms Or 1 mili Ohm

e.g.) IR's family of StrongIRFET as an example.


Jim Ford
 

Yeah, a tenth of a milliohm raised my eyebrow!Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: garp66 <@green> Date: 1/6/20 3:10 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Tek 576 Curve Tracer solid state replacement for relays ? Sorry,   typo correction:   Not 0.0001 OhmRDS of 0.001Ohms   Or  1 mili Ohme.g.)  IR's  family of StrongIRFET as an example.


Brad Thompson
 

garp66 wrote on 1/6/2020 6:03 PM:

hi

Still I wonder if *any* of the Tek 576 relays could be replaced with power Mosfets.
I am curious if some Hexfet / Mosfet relay replacement(s) might then be more reliable ?

Brad:
Are all of the relays in the Tek 576 that you are referring to susceptible to the issue you have brought up ?

I have used a number of different power Hexfets , Mosfets made by IR ( IRF.com ) , having very low "On" resistances ( 0.0001 Ohms ) at various voltages. These Fets are capable of being turned 'on' via the output of a single TTL gate, without issue. I have also placed these in series or parallel (D-S) to achieve a wider ranges of specification with good results.
Hello, Rick--

Thank you for your comments. I have an ailing 577 awaiting attention, but I haven't studied its
schematic with an eye toward replacing relays with MOSFETs nor have I done the same with a 576.
Thus I'd be guessing about the feasibility of making *any* replacements.

It would be interesting to hear from someone who was involved with design of Tek's more-recent
curve tracers. Are there reliability issues that would justify the time spent in reverse-engineering the relays
followed by forward-engineering the MOSFET replacements?

73--

Brad  AA1IP


garp66
 

hi Jim,

Actually, sub milliOhm RDS ( µRDS(on)FET™ series ) Mosfets *are* a reality now with Picor's PI2002, RDS @ ~ 360µΩ
, and the PI5101, @ ~ 0.7 milliOhm but at lower voltages.
So we are getting there !

https://www.powerelectronics.com/technologies/discrete-power-semis/article/21858172/submilliohm-mosfets-onstate-voltage-drop-is-only-279-mv-at-50a


Anyway, my main query was to 'thought provoke' a Mosfet or Hexfet replacement to aging relays in the Tek 576 Curve Tracer :
a) For improved reliability & functionality over problematic dying or dead relays, since Tek replacements won't be available forever.
&
b) A solid state replacement for the mechanical relays also might allow a method for possible automation of the Tek 576 switch settings, for external CPU monitoring and control of the CT.

I would think that standard Mosfets with an RDSon in the milli-Ohm range could be pasted-in to the Tek 576 relay circuits without great trouble ?

Are there any Tek 576 Relay experts out there who could chime-in ??
rick


Jim Ford
 

Good to know!  Thanks.JimSent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: garp66 <@green> Date: 1/7/20 8:14 AM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Tek 576 Curve Tracer solid state replacement for relays ? hi Jim,Actually,   sub milliOhm RDS ( µRDS(on)FET™ series ) Mosfets  *are*  a reality now with Picor's PI2002, RDS  @ ~  360µΩ ,  and the PI5101,  @ ~ 0.7 milliOhm but at lower voltages.So we are getting there !https://www.powerelectronics.com/technologies/discrete-power-semis/article/21858172/submilliohm-mosfets-onstate-voltage-drop-is-only-279-mv-at-50a>>  Anyway, my main query was to 'thought provoke'  a Mosfet or Hexfet  replacement to aging  relays  in the Tek 576 Curve Tracer :a)  For improved reliability & functionality over problematic dying or dead relays, since Tek replacements won't be available forever.&b)  A  solid state replacement for the mechanical relays also might allow  a  method for possible  automation of the Tek 576   switch settings, for external CPU monitoring and control of the CT. I would think that standard Mosfets with an RDSon in the milli-Ohm range could be pasted-in to the Tek 576 relay circuits without great trouble ?>> Are there any Tek 576 Relay experts out there who could chime-in ??rick


DaveH52
 

On Mon, Jan 6, 2020 at 05:01 PM, garp66 wrote:


Tek 576
I'm sure it could be done, however, you'd need to use some sort of isolator-gate-driver for each set of contacts you want to replace. Such devices do exist.
https://www.analog.com/en/products/interface-isolation/isolation/isolated-gate-drivers.html#
but it might be easier to find relays that will fit the same footprint.


KB6NAX
 

I have no knowledge of the 576 circuits but it is conceivable if the voltages are within limits an analog transmission gate could replace an electro-mechanical relay. Of course the "on" resistance would be not less than tens of ohms and could be in the 100's so the gate has to drive a very high resistance load to minimize errors. An example of a commonly found transmission gate is the CD4066. Looks like replacing bad with good relays is the best remedy for the 576. -Arden