Realize two partial pressure circuit classical methods are to use the equal resistor of two pieces of hindering value. If use the precision as 1% of the resistors, the voltage precision of output of two partial pressure device is 2%. As to the thing that the great majority should be used and, this precision is economical and practical, enough to meet need. However, when you need extremely high precision, this kind of method needs corresponding and accurate resistor, therefore may need to increase the cost. Give to the amplifier of the instrument in addition, feedback the return circuit, can obtain a piece of two partial pressure circuit, have advantage outputted to buffer ‘ Fig. 1 . The operation principle of this circuit is very simple. The amplifier of this instrument has the characteristics that the unit gain, so the voltage on its input terminus appears between VREF and VOUT; VOUT-VREF =VIN -VIN- . However, in view of the illustrated circuit of Fig. 1, please pay attention to VOUT =VIN- ,VREF =0. Taking the place of into the first formula, you can get VOUT =VIN -VOUT, 2VOUT=VIN ,Namely VOUT =1/2 VIN . So, you obtained a piece of two partial pressure circuit. One of the interesting characteristics of this circuit is, the unregulated voltage of input and outputting the unregulated voltage of the amplifier of the instrument is reduced by half too.
You can realize this kind of two partial pressure circuit with LT1167 type or Model LTC2053 instrument amplifier at the working bench ‘ Fig. 2 . Though the working bench tests it is unnecessary, you can introduce RC network in feedbacking the thorough fare, by having a facelift to the noise and guaranteeing the performance of main limit. Unregulated voltage in that LT1167 for testing, it want VIN Set up as 0V, let VIN – Change alternatively between 0V and VOUT. This test proves, feedbacking makes the total unregulated voltage reduced by half. , at 5V, output of LT1167 100μ V in error the intersection of 10V and partial pressure. Use accurate LTC2053 the intersection of 2.5V and partial pressure as 1.25V, its output error, for 2.5μ V, measure, come out nearly. While using cold spray gun and hot spray gun, this error may increase to 15μ V. However, perhaps the result of calculation of the worst situation is likewise important.
It shows that the worst situation of LT1167 is calculated, while inputting for 10V, exporting as 5V, within the range of temperature of 0~70 ℃, the biggest error is 1.12mV. The total error in the temperature range that this maximum error value forms is 224