FI87861B - EN AUTOMATISKT SIN FOERSTAERKNING REGLERANDE INSTRUMENTERINGSFOERSTAERKARE - Google Patents

Description

1 87861

An instrumentation amplifier that automatically adjusts its gain. - It is automatically authorized for use in the provisioning of funds.

The invention relates to an instrumentation amplifier of the type defined in the preamble of claim 1.

I instrumentation amplifier I la means a device that measures often weak analog voltages from different sensors. 10 The amplifier is currently built with a few operational amplifiers, but can also be implemented with UJT and FET transistor amplifier stages. The output signal of the instrumentation amplifier is usually measured by means of an analog-to-digital converter connected to a computer, which converts, for example, the output voltage of the amplifier output-15 0 to 5 V to correspond to numbers 0 to 1023- In certain applications the level of the measurement signal varies greatly e.g.

10 mi from 11 {volts to 5 volts, or three orders of magnitude. If the measuring range of the analog-to-digital converter used in the computer is 0 to 5 V, the low voltage range cannot be measured with sufficient accuracy.

In the exemplary case, with a converter having a resolution of 1000, the signal signals can no longer be measured with any accuracy, even though the inherent resolution of several analog signals is of the order of one per thousand. In practice, the solution currently used is a so-called logarithmic amplifier, the output voltage of which is the logarithm of the weathering voltage. The problem is that the logarithmic amplifier has to be built with a forward diode, which is very temperature sensitive. The temperature-drift of the amplifier must be compensated for in one way or another, for example by means of a temperature-dependent resistor, i.e. a thermistor. In practice, a 30 logarithmic amplifier becomes, complicated in structure and expensive. In applications with a large number of sensors, price Much determines usability.

The object of the invention is to develop a simple and inexpensive instrumentation amplifier which can measure the 2 87861 analog signals given by the sensors with sufficient accuracy, even if the signal size varies by several orders of magnitude.

The greatest advantage of the invention can be considered to be the cheapness which results from the use of simple basic components. The amplifiers according to the invention avoid the high temperature dependence of logarithmic amplifiers which is difficult to compensate for.

In order to achieve the above effect, the invention is mainly characterized by the features set forth in the claims.

Figure 1 shows the principle of the amplifier and one of its implementation solutions at the component level.

In the invention, the instrumentation amplifier, Fig. 1, is implemented in such a way that the amplifier automatically changes the gain until the output signal is always between, for example, 1 to 10 volts. The amplifier can be used to measure the voltage range from, for example, one millilecond to ten volts with practically the same accuracy. The amplifier can be constructed with simple basic components, which makes it difficult to compensate for a large temperature drop, as is not the case in a logarithmic amplifier. The amplifier 1 is feedback by means of the multiplexer 2 and the resistors 3 so that one resistor at a time is connected between the output and the input of the amplifier.

25 The multiplexer is controlled by lines k. The control lines are connected up / down to counter 5. The output voltage of the amplifier is compared with a reference voltage of 7 volts by means of a comparator 6. If the output voltage is less than 1 volt, the output of the comparator goes to 1 and the counter value increases. The output lines 4 30 * of the counter 5 control the multiplexer 2, which changes the channel by selecting a magnifying feedback resistor 3. Due to the strong feedback, the output of the amplifier is always above 1 volt. The gain of the amplifier can be read into the computer by the output 5 of the counter 5. ; the input lines.

3,887,861

The invention has been described above with reference to a very simple embodiment, to which the invention is by no means limited, but can be modified within the scope of the claims. In practice, the amplifier can be implemented by means of several different components 5. For example, the multiplexer can be replaced by other logic circuits.

Claims (2)

1. An automatic gain control instrumentation amplifier, which feedback of the amplifier (1) is formed by parallel resistors (3), one of which is coupled at a time to determine the amplifier's amplification factor by comparing the output with a reference voltage (7) several times. , by always switching resistor (3), that the measurement signal exceeds the selected reference voltage, and while the signal's amplified value is read, the gain factor or resistor (3) abandoned to characterized in that the amplification (1) of the amplifier (1), which determines the irresistible feedback resistance (3), is coupled via a multiplexer (2) or via logic circuits which are controlled (4) with an up / down counter (5), as in in turn, follows the condition of a comparator (6) until it, when it observes that the reference value has been exceeded, stops the counter (5) and the feedback resistor is fixed, refts the output voltage of the amplifier (1) and the gain factor or resistor (3) is read from the output lines of the up / down counter (5). "·· <· 2. An amplifier according to claim 1, characterized in that, in parallel with the comparator (6), a second upper limit comparator is coupled to the maximum output voltage and that it lets the up / down counter count in the other direction if the voltage in the instrumentation amplifier output rises too high. φ »·