• In a noisy environment to protect digital temperature sensor (20)

  • It is difficult to adopt the digital temperature to detect the method in the noisy environment. The noise is apt to couple to the sense slowdown monitoring circuit of temperature and may cause the great temperature error. In fact, a very strong noisy environment may totally submerge thermometry, make any result useless. And to make matter worse, it has already been impossible for this kind of application to increase an electric-wave filter meeting the demands on the forward end of the digital sensor up to now. This is because electric capacity and resistance related to electric-wave filter interfere with used measurement technique, result in deflecting, cause the consequential error of the temperature. It means it has already no longer been this kind of situation that the series resistance imbedded in the latest digital sensor compensates technology. For example D + and D - it increases 1 simple R-C-R electric-wave filters to be to or dispels noise effect (meet picture 1) in the thermometry input, in ADT7461. The long-range sensor is that a connection becomes the standard pnp transistor of the diode. Its emitter is connected to D + pin of ADT7461, and base electrode and collecting electrode are connected to D - input. The electric-wave filter is made up of two resistors and a 1nF capacitor of 100Ω. It is possible close to D + and D - input to put the electric-wave filter. This filtering utensil 1.6MHz alpha cut frequency. Without electric-wave filter, the error in emasurement of the temperature may reach 80 â,,ƒ or more greatly. It is possible that it makes the error lower to below 1 â,,ƒ that there are electric-wave filters, it is ideal that this kind of circuit configuration is applied to the noisy environment. Can construct the electric-wave filter with other resistance and capacitance value according to required alpha cut frequency. Maximum capacitance value restrict 2.2nF to, because any electric capacity of high-value can influence thermometry relatively. Likewise, limit in 3KΩ as to D + and total resistance quantity of D - thorough fare. Usually, any resistance on the thorough fare will influence the metric precision of the temperature among long-range sensor and digital temperature sensor of standard. Generally, have 0.5 â,,ƒ deviation with the metric temperature value of each ohm of the sensor cascade connected stray resistance. However, ADT7461 dispels the influence up to 3KΩ series resistance automatically. This kind of characteristic allows to put the electric-wave filter between ADT7461 and long-range sensor. The electric-wave filter in Fig. 1 shows that + and 100Ω resistance in D - thorough fare in D to the external sensor. Users do not need to finalize the bid. In addition, any resistance related to other interface units of wired and of mark of p-c board will be dispelled too, this allows to put the long-range temperature sensor at the place where far away from ADT7461 certain distance. Fig. 2 shows how valid electric-wave filter is in strong noisy environment. The noise in this embodiment is 100MV rectangular wave, add from the phase equality to D + and D - thorough fare. When not putting the electric-wave filter, the error in emasurement of ADT7461 temperature is up to 50 â,,ƒ. It is impossible that this kind of noise level adopts the temperature to control IC when not having electric-wave filter in the system. Depend on, adopt electric-wave filter, can make error drop to less than 1 â,,ƒ, lower than device it marks to be

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