北京康泰电子有限公司

问题：1、单端输入和差分输入有什么区别？

答： Single-Ended Inputs Single-ended inputs connect one wire from each signal source to the data acquisition system. The data acquisition system then simply measures the DIfference between the signal and the ground (or earth) at the PC. This requires that the signal source is grounded (earthed), and is the same value as that at the PC. DIfferential Inputs DIfferential inputs use two signal wires from each signal source to the data acquisition system. One connected to the positive input and one to the negative input. The voltage between the input and the PC ground is monitored by two high-impedance amplifiers. A third amplifier is used to measure the DIfference between the +ve and -ve inputs, eliminating any voltage common to both wires. This method eliminates the problems that can occur with a single-ended system. That is any DIfferences in grounds are irrelevant, and noise can be reduced; using twisted pairs ensures that any noise generated will be the same for each wire. Pseudo-DIfferential Inputs Some data acquisition boards claim to be DIfferential but are in fact pseudo-DIfferential inputs. This is acceptable provided the signal sources are close together and do share a true common ground. Pseudo-DIfferential is similar to single-ended with the ground of the signal isolated from the PC. The Source ground is then connected to the PC ground, by measuring the DIfference between these two grounds; the effect of this DIfference can be removed from the measurement. However, pseudo-DIfferential inputs can not eliminate the effects of noise. Choosing between single-ended and DIfferential inputs DIfferential is best when - Signal leads are over a few metres in length This eliminates the effects of noise pick up and the possibility of ground DIfferentials - Measuring small signals under around 100 mV These can be overwhelmed noise and ground DIfferentials - Measuring output from sensors with high impedance such as strain gauges. DIfferential inputs remove common mode voltage. High impedance can lead to higher common mode voltages. Single ended is appropriate - When you want a low cost system to measure a lot of input signals and youare confident that the above situations can be eliminated.