DETECTION DEVICE AND THICKNESS MEASURING DEVICE

To protect a receiving amplifier while reducing an influence on measurements using eddy currents.SOLUTION: A processing device 6 includes: a first detection coil 13 and a second detection coil 14 connected in series; a receiving amplifier 51 to which the first detection coil 13 and the second detection coil 14 are connected; and a protection circuit 52 connected in parallel to the first detection coil 13 and the second detection coil 14. The protection circuit 52 includes: a first protection circuit 52A that includes a first resistance element 53a and a first diode 54a connected in series, and is connected in parallel to the first detection coil 13 between a first end 13a and a second end 13b of the first detection coil 13; and a second protection circuit 52B that includes a second resistance element 53b and a second diode 54b connected in series, and is connected in parallel to the second detection coil 14 between a first end 14a and a second end 14b of the second detection coil 14.SELECTED DRAWING: Figure 6 【課題】渦電流を用いた測定に与える影響を低減しつつ、受信アンプを保護する。【解決手段】処理装置６は、直列接続された第１検出コイル１３及び第２検出コイル１４と、第１検出コイル１３及び第２検出コイル１４が接続された受信アンプ５１と、第１検出コイル１３及び第２検出コイル１４に並列に接続された保護回路５２とを備えている。保護回路５２は、直列接続された第１抵抗素子５３ａ及び第１ダイオード５４ａを含み、第１検出コイル１３の第１端１３ａと第２端１３ｂとの間に第１検出コイル１３と並列に接続された第１保護回路５２Ａと、直列接続された第２抵抗素子５３ｂ及び第２ダイオード５４ｂを含み、第２検出コイル１４の第１端１４ａと第２端１４ｂとの間に第２検出コイル１４と並列に接続された第２保護回路５２Ｂとを有する。【選択図】図６