Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Converting input voltage to output current or vice versa
Patent
1996-06-13
1998-06-23
Tran, Toan
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Converting input voltage to output current or vice versa
327336, 327101, H03C 300, G06G 764
Patent
active
057709564
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention relates to a measurement amplifier.
BACKGROUND OF THE INVENTION
Charge balance amplifiers are known which supply an output voltage, the frequency of which is proportional to the input current. The known charge balance amplifiers have an integrator which includes an integrating capacitor. Moreover, the known charge balance amplifiers have a reference current source. The reference current source supplies a reference current to an input node for a pre-defined period of time, if the voltage appearing at the output of the integrator exceeds or falls below a reference voltage level. With the reference current source active, the capacitor discharges. The frequency at which the charging and discharging process occurs is proportional to the input current.
If such a charge balance amplifier is employed in the measurement of very weak currents, the frequency is very low so that the acquisition of the measurement data is problematic. Variations in the input current which is to be measured can not be immediately detected since the time for the charging process is too long at very weak input currents.
SUMMARY OF THE INVENTION
It is the task of the present invention to create a measurement amplifier which permits rapid acquisition of the measurement data.
In the measurement amplifier according to the present invention a circuit is provided which receives the voltage which appears at the output of the integrator. This circuit may be a differentiator, for example. The differentiator supplies an output voltage which is proportional to the variation in time of the voltage. The output voltage of the differentiator is proportional to the input current of the measurement amplifier which is to be measured. Moreover, the voltage variation can be performed also through the measurement at two points of time, at least.
The measurement amplifier according to the present invention permits the acquisition of very weak currents and may be employed, for example, in the area of vacuum technology for the measurement of the ion currents generated by an ionization vacuum gauge, where said currents have an order of magnitude beginning at approximately 10.sup.-15 A.
The output of the differentiator is preferably processed when the reference current source has been switched off and when the integration capacitor is being charged. From the variation in time of the voltage occurring at the output of the integrator it is possible to conclude as to the magnitude of the input current. The greater the input current, the faster the output voltage of the operational amplifier will attain the level of the reference voltage.
Moreover, in the acquisition of very weak currents there arises the problem that the output voltage of the circuit operating as an integrator, for example, an operational amplifier, and the switch of the reference current source are influenced by a fault or leakage current which varies over time. To detect the fault current, a capacitor may be connected in series with the input of the operational amplifier. Moreover, a switching component is provided which, when closed, shorts the capacitor. From the difference in the measured voltage variation at the output of the integrator when the switching component is open and closed, it is possible to determine the fault current. For the purpose of compensating the fault current, a compensation current source is preferably provided which supplies an adjustable compensation current which is applied to the input of the circuit used as an integrator. In the case of a correctly set up fault current compensation, the compensation current is set up in such a manner that the output voltages of the operational amplifier operating as a differentiator are equal when the switching component is closed and open. Through opening and closing of the switching component, and by changing the magnitudes of the compensation current, it is possible to entirely compensate the fault current.
Moreover, there is the possibility of not, or only partly compensating the fault curre
REFERENCES:
patent: 3944920 (1976-03-01), Borer
patent: 4620148 (1986-10-01), Davison et al.
patent: 4697151 (1987-09-01), Butler
patent: 4839788 (1989-06-01), Tullsen
patent: 4992673 (1991-02-01), Gessaman et al.
patent: 5585748 (1996-12-01), Yamaguchi et al.
Nullpunktfehler des Operationsverstarkers, 1973; pp. 123-126.
Leybold Aktiengesellschaft
Tran Toan
LandOfFree
Measurement amplifier does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Measurement amplifier, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Measurement amplifier will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1397161