![]() The LTC1090 with its serial architecture is ideally suitedįor isolation applications. Opto isolators such as Hewlett Packard’s HCPL2200Īre available which can transmit data at the full 1MHz Such as Sprague or Pulse Engineering, or high speed Transfer rates, pulse transformers from companies Transferring serial data at about a 15kHz rate, which The circuit demonstrated in Figure 1 is capable of Time CS goes low and the first SCLK edge is generated.Īnother delay of 44 ACLKs is required during the time Provide a delay of at least two ACLK cycles between the The frequency of the ACLK generated by the 74C14 is not too critical. Nine channel readings are required because, when the LTC1090 is powered up, a dummy read is necessary to Powers down until the next set of readings is required. To its final value, reads 9 channels in 12ms, and then Up the circuit, allows 6.0ms for the 10μF cap to charge The code written for the Motorola 68HC05 processor Output transistor is there to decrease the turn off time Of the opto isolator must have enough base current toĭrive the desired load. Opto drivers are chosen with the Current Transfer Ratio The current limiting resistors in the collectors of the Rates or if burning more current is not objectionable. LTC1090 in time to be captured by the processor on the This insures that DOUT can be output by the SCLK have as little delay as possible through the opto It is therefore necessary that the falling edge of LTC1090 is transmitted on the falling edge of SCLK.ĭata is clocked into the processor on the rising edge of ![]() To optimize signal fall time and clock rate. PNP transistors were chosen to drive the opto isolators Micropower, 500V Opto Isolated, Multichannel, 10-Bit Data Acquisition System is Accessed Once Every Two Seconds. If more isolation is desired, up to 2500V of isolationĬan be obtained by using 4N25s with no other circuitįigure 1. They provide only 500V of isolation, however. The 4N28s in Figure 1 are very commonly used opto The LT1021 powers the analog circuitry and provides anĪccurate reference. Up to 24Ĭhannels can be powered directly by the LT1021. The number of channels in multiples of eight. The number of channels can be increased to 16, 24, 32,Įtc., with one additional opto isolator used to increase With the addition ofĪnother opto isolator, the circuit can be battery operated, drawing only 50μA while taking a reading once The circuit to be demonstrated is an eight channel dataĪcquisition system with 500V of isolation that uses the Transformers, they will be the only type of device However, since opto isolators tend to be smaller and less expensive than pulse EachĪdditional eight channels requires only one additionalīoth opto isolators and pulse transformers could be Now, with the LTC1090 family of serial dataĪcquisition systems, it is possible to transmit eightĬhannels of data with only four isolated lines. Traditionally, the highly noise immune, digitallyĮncoded signals required many isolated lines for eachĬhannel. Immunity and one isolator is required for each signal ![]() The data transmitted over the isolated lines can beĮither analog or digital. ![]() Points and the system controller which can cause errors. Include the following: to allow floating measurementsĪt high voltages for safety, to reduce the danger ofĮlectrical shock, as might occur in medical applications Īnd to eliminate ground loops between measurement In data acquisition systems it is often necessary toĮlectrically isolate the measurement points from the William Rempfer Download PDF Introduction Design Note 10: Electrically Isolating Data Acquisition Systems
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