Clampon Earth Resistance Meters

Hi Experts, 

I am working on developing a design that can measure loop earth resistance of the Earth Pits. Fundamentally, I know that the induced current in the magnetic core is directly proportional to the resistance of the earth. So I will need one voltage induction circuit that can induce some constant Sine Wave Voltage with a specific frequency and on the other core I detect the induced current, measure it and derive VI relation to figure out the resistance. 

But  I did not find any reference circuits for the same. So can someone help me with the detailed design considerations? 

1. What would be the magnitude of the induced voltage? 

2. What will be the injected signal frequency? 

3. What type of magnetic core should I be using? Can someone suggest me, good vendors? 

4. What will be the injected signal current? 

5. Which low-power ADI parts should I be considering for both injection and detection circuits? 

Most importantly, this will be a battery-powered device, hence can the entire circuit be driven from Lithium battery - single cell? 

Best Regards, 

Rahul