I propose you use a dual battery operated measurement device with 200dB CMRR when you are using high impedance signal sources and high impedance loads (OA) you can use large divider ratio ( 10~30:1) then amplify with a single resistor to choose any gain you want 1~1000.
Why?
Because E-field from AC mains will be high; and ESD events can be 10~25KV E-fields from just connecting the cables to the sensor..
Just touch any 10MΩ*probe and you can get 80Vac from a 120Vac line. You want possibly 100:1 to 1000:1 SNR on all scales from +/-1 to +/- 100V..
How?
1. First choose a 3 OA configured IA (Instrumentation Amp) with 130 to 140db CMMR over range.
2. Choose signal bandwidth.. unless just DC and add active LPF to differential IA chip feedback and plan on using some differential LPF
3. Choose a CM choke that will provide 60~70 dB CM rejection over 50/60Hz and up to LPF cutoff.. If not go for 40dB... THis will be the highest permeability ferrite avail. often found on USB cords, mic cords, charger DC cords and come in any sizes & shapes from wound torroid.. dual donut hole to clam-shell donut torroids. (best) All your wires can be small wire gauge or even Litz wire or stranded 24 AWG to 26AWG in twisted pair shielded and run through or around donut CM choke several turns or use thin wires without jacket to wrap around CM choke then seal with PolyUrethane potting or Epoxy. or for a prototype PL400 sub-floor adhesive that will turn rock hard and is cheap. Then run cable jacket over twisted pair bundled.. or consider using subminiature Coax if you opt out of the differential design ( Cable suppliers use clamshell types and then mold in hard PU material or hard PVC to protect brittle ferrite.
BTW: You cant use ethernet magnetics because they don't work well at 60Hz as well as they work at 1:10:100:1000 MHz.. and you need CMRR for 60Hz.
4. Then choose dual batteries such as 3V Lithium $1.5 ea CR123 socket $1.5/pc by the dozen at Home Depot.
5. Then get Battery receptacles for CR123.
6. Then design gain and LPF active filters using your 200 dB CMRR precision Instrumentation Amplifiers ( commonly used for low EEG signals on noisy body with galvanic skin DC offsets. with 50uV and > 40dB SNR
7. Look here for a wide selection of I.A.'s
https://www.linear.com/products/instrumentation_amplifiers
8. Look here for Lithium batteries 1500 mA-hr
https://www.homedepot.com/buy/tools...-lithium-3-volt-batteries-12-pack-188349.html
9. Don't forget to prevent battery ejection lids.
10. Consider putting it in a tinned brass shield soldered onto PWB and then mount inside a plastic box preferably conductive ESD/EOS safe plastic...
11. Ensure you put in TVS to protect the IC's on every signal input and choose your termination resistance to be whatever you want 10MΩ probe like with tuned cap to offset cable capacitance or whatever going into 2MΩ input load for 50:1 divider.
12. Use good plastic low ESR polyester caps across battery (1~100mΩ) that are not microphonic like ceramic... or cheap alum. high temp. 2nd best.
13. Dont forget switch and power indicator using 3mA of a 20Cd white or Blue LED that runs off 3.2V .. 20mA will blind you... so 3 Vdrop over 3mA will plenty bright. with 1KΩ.. To get fancy make a low voltage indicator using Schmitt trigger inverter which changes pulse repetition rate with battery voltage... any inverter cap. to ground and 1~10MΩ feedback resistor on low leakage cap. say 1Hz blink.. use pull-up input bias resistor for 10% duty cycle on full charge and 1% on end of battery life 1 to 10Hz .... or better yet use two blue LEDs in series on 6V which is ~6.5V new and ~5.5 dead so LEDS go out when battery is dead and use 470Ω i series with 2 LEDs. 2~3mA new. battery 0.5mA dead... Close enough for 1st estimate.
You got 1500mA-hr...
14. Then test your design with CM noise pulse and differential signals with zero input. for SNR and all the other tests.. Vbat noise sensitivity. drive a signal to see PSRR. etc etc... calc battery life... .. write user manual...and theory of operation spec.
{Farmout design layout so a good analog PWB designer.} or do yourself.
15. When happy.. go for a soda.
https://www.linear.com/product/LT1167
OK maybe the 200dB is ambitious.. but I hope you got my point.. Overdesign and hope it works at worst case.
10 kV CM /1uV Diff Mode = 200dB I guess that is overkill...if you just measuring big signals such as +/1V and +/-100V but then my assumption may have been wrong that you needed 10 bit resolution and accuracy.
Comments?
Total cost.. cheap... Your time... expensive...
High impedance Scope like accuracy on long probes with high impedance source.
Ref my selection of high CMRR I.A's
Product Channels (#) Vos (uV) Vos TC (uV/C) CMRR (dB) Vs Min (V) Vs Max (V) Comments Packages
LT1167 1 15 0.05 140 4.6 40 Precision, Low Bias Current IA DIP-8,SO-8
$6.45 ea
LT1167-1 1 15 0.05 140 4.6 40 Precision, Low Bias Current IA, Controlled Input Current at High CM Volt and Hi Z SO-8
LT1168 1 15 0.05 140 4.6 40 Precision IA, Low Bias Current, Low Power DIP-8,SO-8
LT1920 1 30 1 140 4.6 40 Resistor Programmable IA DIP-8,SO-8