[ Specified attachment is not available ]I especially despise this kind of behavior！
(Attachment Link) I especially despise this kind of behavior！
Where are these photos from? Is there any discussion on another forum? Or a review?
Rotated so its easier to compare
Interesting how Tonghui skimped on the guard ring around the (presumably very high impedance) nodes with the high value thin film resistors to the point where the ring around R103 has barely any copper around the vias. Funny how on the Tonghui board they added footprints for extra resistors in case they needed to adjust something, while Keysight probably had the resistors made to spec. It also looks like the the TH board might have fewer layers, although that could be the lighting.
They replaced the main part
The vacuum capacitor was replaced with some kind of rubbish.
There is obvious similarity in the layout, but there are still differences: the Tonghui meter has 1 range less and the case / connectors are also different with inputs at the front instead of the back.
A decade lower sensitivity also means they can get away with more.
The extra footprint for a 2nd parallel high ohms resistor is odd, expecially with the same size. It would make some sense for a different size, but not this way. For a trim a sereis resistor is there an much more conventient.
Somehow both designs do not try to really keep the critcal node compacs / small.
The extra footprint for a 2nd parallel high ohms resistor is odd, expecially with the same size. It would make some sense for a different size, but not this way. For a trim a sereis resistor is there an much more conventient.
The bottom one is marked as a capacitor.
Top one I can't see.
The 3pF capacitor is a vacuum type? Do you have a partnumber/datasheet for it MegaVolt?
Tonghui should not understand the key technology of low current measurement.
Lol, still managed to clone it, even with service manuals unavailable.
Take that Keysight and anyone else with no schematics available, for making honest repairs much more difficult.
A comment on both boards. It is curious to see all the guarding, and cutouts, while also employing signal relays (datasheet suggests 1G insulation resistance), rather than reed relays.
Maybe the signal relay coils, and pole node, are driven by isolated/floating signal relays. The digital board of the agilent has a bunch of reed relays, so perhaps that is the strategy used.
A comment on both boards. It is curious to see all the guarding, and cutouts, while also employing signal relays (datasheet suggests 1G insulation resistance), rather than reed relays.
The AGN210 series relays are adequate for the application of this device. They have an insulation resistance between open contacts > 100 PetaOhm and an insulation resistance between the coil and all shorted contacts > 100 TeraOhm. (Data from actual measurements of a certain number of these relays)
These relays also provide reliable contact for switching low currents/voltages.The main disadvantage of these relays is the absence of an electrostatic shield between the coil and the contact groups, so that they have a very high charge injection from the control (when the relay is switched).
P.S. The Hongfa relays used in the Tonghui electrometer have comparable parameters with the Panasonic AGN210 series relays
P.P.S. For comparison, the insulation resistance between the open contacts of the electrometric reed relay TRY-204S-14 manufactured by Okita is about 2 PetaOhm
A comment on both boards. It is curious to see all the guarding, and cutouts, while also employing signal relays (datasheet suggests 1G insulation resistance), rather than reed relays.
The AGN210 series relays are adequate for the application of this device. They have an insulation resistance between open contacts > 100 PetaOhm and an insulation resistance between the coil and all shorted contacts > 100 TeraOhm. (Data from actual measurements of a certain number of these relays)
These relays also provide reliable contact for switching low currents/voltages.
The main disadvantage of these relays is the absence of an electrostatic shield between the coil and the contact groups, so that they have a very high charge injection from the control (when the relay is switched).
P.S. The Hongfa relays used in the Tonghui electrometer have comparable parameters with the Panasonic AGN210 series relays
P.P.S. For comparison, the insulation resistance between the open contacts of the electrometric reed relay TRY-204S-14 manufactured by Okita is about 2 PetaOhm
Hi, thanks for your information.
I wonder if the same series AGN200 relays (single side relays) have the same insulation performance as the AGN210 series? In my design, it's a bit difficult to provide polarity-reversed driving signal...
(I have already ordered AGN200S4H, and plan to test its performance when I get it)
And there's another question, what kinds of relays (or key specifications) should be considered first for an electrometer application?
And there's another question, what kinds of relays (or key specifications) should be considered first for an electrometer application?
Reliable contact at low currents; insulation resistance; charge injection when relay switching - preferable shielded relays.
