While designing a data-acquisition system for a government lab, my colleagues and I added an instrumentation amplifier to each of the system's 16 analog inputs. The buyer offered hazy specifications about the low-level signals the lab wanted to measure, so an instrumentation amplifier (in-amp or INA) provided a way to overcome signal problems that might arise later.
Not all data-acquisition systems require an in-amp, but because they amplify small signal differences from transducers and remove large common-mode ac and dc signals in-amps can come in handy. Think of an in-amp as a "gain block" that amplifies signals by an amount you determine. That may sound like a basic op-amp circuit, but an in-amp differs in several ways. First, an in-amp requires only one resistor to establish its gain. Op-amps typically require several carefully matched resistances and resistance ratios. Second, an in-amp exhibits a high common-mode ac/dc rejection ratio, which exceeds that available in most op-amps. Third, an in-amp provides a high input-impedance load, so it works well with many sensors that produce low-level signals that could include an ac or dc component.
The basic in-amp building block comprises three op-amps as shown in the schematic diagram above. In the strain-gauge bridge circuit shown here, one side of the bridge connects to Input 1 and the other side connects to Input 2. As the resistance of the strain gauge changes, the bridge circuit produces a small voltage difference between Inputs 1 and 2. But both inputs also receive a part of the bridge's excitation voltage, V+. Thus, if Input 1 has an applied voltage of 2.000V, Input 2 might have an applied voltage of 2.015V. The 0.015V difference between the two inputs carries the useful strain information. To start, the in-amp precisely and equally amplifies the Input 1 and 2 signals. (In this example, a single external resistor sets the same gain for both amplifiers).
Next, the two amplified signals go to a circuit that subtracts one signal from the other to remove the bridge circuit's 2.000V dc signal common to both inputs. Engineers refer to that as the common-mode voltage because it appears in common at both inputs. An in-amp also can remove common-mode ac signals, perhaps picked up from surrounding circuits, to present a clean signal to an ADC. Note the in-amp converted a differential signal to a single-ended signal. In-amps provide a reference input, so if the need arises you can offset the in-amp's output.
In addition to accurately amplifying low-level signals, monolithic in-amps have other characteristics such as low input bias and low-noise operation. Some in-amps provide fixed gains that users hard wire or set under computer control. So, when you plan your next measurement system, in-amps should get a close look.
Are they robots or androids? We're not exactly sure. Each talking, gesturing Geminoid looks exactly like a real individual, starting with their creator, professor Hiroshi Ishiguro of Osaka University in Japan.
Truchard will be presented the award at the 2014 Golden Mousetrap Awards ceremony during the co-located events Pacific Design & Manufacturing, MD&M West, WestPack, PLASTEC West, Electronics West, ATX West, and AeroCon.
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This discussion will examine what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.