Patent ID: 8115478

Claim:
A device for measuring a concentration of magnetic material comprising a detection unit connected to a passage of flow of or a pool for pooling of fluid containing magnetic material and having inflow/outflow guide means and detection means, and a signal processing unit connected to said detection means and having a lock-in amplifier, said detection unit guiding inflow/outflow of the fluid by means of the inflow/outflow guide means and obtaining a detection signal of magnetic material with the fluid being introduced and a corrective detection signal with the fluid being discharged from an output signal indicative of AC voltage through the detection means, said signal processing unit employing reference signals with the same frequencies as those of the respective signals to noise-remove said respective signals through the lock-in amplifier and detecting phase differences between said respective signals and the reference signals to thereby conduct conversion into DC voltage signals depending on detected phase difference amount, difference of respective values after conversion being detected as concentration of magnetic material.