Instrumentation differential amplifiers

Fig. 4. Impedance converters for measuring e.m.f. of a cell, (A) using a voltage follower (the effective input resistance, equals the common mode resistance of an FET-type operational amplifier), (B) using voltage feedback (Reff R-Ao, where R is the input resistance, Aq is the OA gain without feedback), (C) by means of an instrumentation amplifier (typical differential gain A = 1 + lO /Re t)- Abbreviations OA, operational amplifier AZ OA, automatically zeroed OA lA, instrumentation amplifier S, shielding.

Narrow and broad MW standards were injected onto the HPSEC-DV system at concentrations near 1 mg/mL and 2 mg/mL, respectively. Initially, in order to obtain a usable differential pressure chromatogram, the lignin samples were injected at concentrations near 20 mg/mL, with an instrument (A-D amplifier) gain setting of 1 (0-1.0 volt Full Scale). As the... 

The instrumentation amplifier is a high-performance differential amplifier consisting of a number of closed-loop op-amps. An ideal instrumentation amplifier gives an output voltage which is proportional only to the difference between two input voltages and Vtl, viz. ... 

Figure 9.10. A differential radiometer chopping against a load, using an RF amplifier prior to the square-law detector. This kind of instrument is required when measuring the absolute temperature of the CMB, and was used by Penzias and Wilson, 1965.

Microdielectrometry was introduced as a research method in 1981 14 and became commercially available in 1983 20). The microdielectrometry instrumentation combines the pair of field-effect transistors on the sensor chip (see Sect. 2.2.3) with external electronics to measure the transfer function H(co) of Eq. (2-18). Because the transistors on the sensor chip function as the input amplifier to the meter, cable admittance and shielding problems are greatly reduced. In addition, the use of a charge measurement rather than the admittance measurement allows the measurements to be made at arbitrarily low frequencies. As a matter of practice, reaction rates in cure studies limits the lowest useful frequency to about 0.1 Hz however, pre-cure or post-cure studies can be made to as low as 0.005 Hz. Finally, the differential connection used for the two transistors provides first-order cancellation of the effects of temperature and pressure on the transistor operation. The devices can be used for cure measurements to 300 °C, and at pressures to 200 psi. 

As shown in Figs. 4.8.4 and 4.8.5, typical DTA and DSC apparatus consist of the following basic components (1) furnace or heating device, (2) differential temperature detector, (3) amplifier, and (4) recorder. There are many modifications of this basic design. However, all instruments measure the difference in temperature (DTA) or enthalpy (DSC) between a sample and an inert reference material. 

Brown and Skrebowski [37] first suggested the use of x-rays for particle size analysis and this resulted in the ICl x-ray sedimentometer [38,39]. In this instrument, a system is used in which the difference in intensity of an x-ray beam that has passed through the suspension in one half of a twin sedimentation tank, and the intensity of a reference beam which has passed through an equal thickness of clear liquid in the other half, produces an inbalance in the current produced in a differential ionization chamber. This eliminates errors due to the instability of the total output of the source, but assumes a good stability in the beam direction. Since this is not the case, the instrument suffers from zero drift that affects the results. The 18 keV radiation is produced by a water-cooled x-ray tube and monitored by the ionization chamber. This chamber measures the difference in x-ray intensity in the form of an electric current that is amplified and displayed on a pen recorder. The intensity is taken as directly proportional to the powder concentration in the beam. The sedimentation curve is converted to a cumulative percentage frequency using this proportionality and Stokes equation. 

Texas Instruments, THSA4120, THS4121 high-speed fully differential I/O amplifiers, Datasheet, Texas Instruments, 2001. Analog Devices, AD8132, low-cost, highspeed differential amplifier, Datasheet,... 

A typical DTA apparatus is illustrated schematically in Figure 6.1. The apparatus generally consists of (1) a furnace or heating device, (2) a sample holder, (3) a low-level dc amplifier, (4) a differential temperature detector, (5) a furnace temperature programmer, (6) a recorder, and (7) control equipment for maintaining a suitable atmosphere in the furnace and sample holder. Many modifications have been made of this basic design, but ail instruments measure the differential temperature of the sample as a function of temperature or time (assuming that the temperature rise is linear with respect to time). 

Fig. 11.20 (a) Analogue section of an automated PSA Instrument. The operational amplifiers are NS LF 336. The digital panel meter and the differentiating amplifier are optional, (b) Block diagram of the instrument. PI, parallel interface IRQ, interrupt request. Only 4 kb worth of the PROH capacity is used. Bus transceivers are not shown. (Reproduced from [95] with permission of Elsevier). 

---