the isolated current - frequency conversion circuit to convert 4~20MA to 10KHZ

Published:2011/5/11 7:15:00 Author:Fiona | Keyword: the isolated current - frequency conversion, convert 4~20MA to 10KHZ, | From:SeekIC

Circuit Work This circuit consists of two parts, namely, converting current - voltage section and the use of VF converting voltage into frequency by VF converter section.The current - voltage converter uses a 250Ω resistor R1, produces the voltage at R1's both ends, and then uses OP amplifier 1 to turn the voltage into 0 ~-10V, so the reverse magnification should be 2.5 times. When current is 4MA, in order to make the output of A1 is 0, it must use home bias circuit. It can add the voltage at inverting input to form the home bias. If don't use the method of the home bias,put the in-phase input to ground. It also can be converted to 2 ~ 10KHZ frequency output when A1 magnification is 2. V-F Converter uses NS company's LM331, its detailed structure has been introduced in the company's products' manuals .In order to improve linearity, add the OP amplifier A2, which is the current input type, full range is 0 ~ 100UA, therefore,according to the input voltage range, R5's resistance should be 100K, in the feedback loop, C2's role is to maintain Loop stability, the capacity is selected by range of the input signal.



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