Force transducer

Figure 4. Experimental setup for stress-relaxation and cross-linking at constant simple extension. Key A, electron accelerator B, beam aperture C, force transducer D, thermostated box E, sample F, stretching device G, connecting rods.

Using a standardized method for eliciting flexion (electrical stimulation of the base of the hindpaw) and a quantifiable method of contraction measurement (force transducer attached to the hindpaw), Nozaki et al. (136,137) found that LSD (10 Mg/kg) and tryptamine both increased the flexor reflex in acutely spinalized rats. Both these effects were blocked by pretreatment with the 5-HT antagonist cyproheptadine. A similar LSD effect was reported in spinal cats (118). 

In preparation for the screen, a sufficient number of scoring sheets are filled in with the appropriate information. Then the cart employed as a mobile testing station is checked to ensure that all the necessary equipment (empty wire-bottom cage, blunt probe, penlight, 1/2 in. diameter steel rod, force transducer, ink pad, pad of blotting paper, ruler, and electronic probe thermometer) are on the cart and in forking order. Each animal is then evaluated by the following procedures. 

Further aluminum pour tests were made in a heavy-wall stainless steel tank fitted with Lucite side windows. The tank was supported on a force transducer and pressure transducers were located on either end. In a test, after the spill, there was a predetermined delay and then the wire was exploded. The aluminum usuaUy had puddled on the tank bottom before the wire explosion and steam bubbles could be seen. The shock from the wire explosion usually collapsed the film and, following this, the aluminum expanded. If the shock were sufficiently energetic, the aluminum soon fragmented and expelled the water from the tank in a thermal explosion. In such cases, the force transducers on the bottom ranged from 5 to 10 N sec. (The exploding wire alone led to impulses around 1 N sec.) Efficiencies of an explosion calculated as indicated above were low. 

S. B. Smith, Y. Cui, and C. Bustamante, An optical-trap force transducer that operates by direct measurement of light momentum. Methods Enzymol. 361, 134-162 (2003). 

Figure D3.6.1 General principle of direct force-transducer-based tensiometers (Wilhelmy plate and/or du Nouy ring method). I/O is input/output.

The basic setup to determine static interfacial tension based on either the Wilhelmy plate method or the du Noiiy ring method (see Alternate Protocol 2) is shown in Figure D3.6.1. It consists of a force (or pressure) transducer mounted in the top of the tensiometer. A small platinum (Wilhelmy) plate or (du Noiiy) ring can be hooked into the force transducer. The sample container, which in most cases is a simple glass beaker, is located on a pedestal beneath the plate/ring setup. The height of the pedestal can be manually or automatically increased or decreased so that the location of the interface of the fluid sample relative to the ring or plate can be adjusted. The tensiometer should preferably rest on vibration dampers so that external vibrations do not affect the sensitive force transducer. The force transducer and motor are connected to an input/output control box that can be used to transmit the recorded interfacial tension data to an external input device such as a monitor, printer, or computer. The steps outlined below describe measurement at a liquid/gas interface. For a liquid/liquid interface, see the modifications outlined in Alternate Protocol 1. Other variations of the standard Wilhelmy plate method exist (e.g., the inclined plate method), which can also be used to determine static interfacial tension values (see Table D3.6.1). 

Using forceps, attach the clean platinum Wilhelmy plate to the hook that is connected to the force transducer or pressure sensor mounted in the top of the tensiometer. Do not touch the plate, and make sure that the plate does not yet touch the surface of the sample. 

Lower the pedestal until the plate just detaches from the interface and wait until all plate movement has stopped. Zero (tare) the force transducer or pressure sensor. 

Wait until the interfacial tension shown on the electronic display no longer varies due to the movement of the ring, and zero (tare) the force transducer. 

However, to improve reproducibility for forelimb grip strength we recommend orienting the force transducer vertically (Columbus Instruments, Columbus, OH, USA) and modifying the test procedure as follows. A weight (100 g) is attached to the base of the mouse s tail using a small plastic clip. The mouse is held by the scruff of the neck with the tail and weight in the... 

Contractile properties in rodents can be measured either in vitro in a dissected muscle or in vivo in an intact preparation with an anesthetized animal (e.g., (19-20)). Measurements made under isometric conditions are perhaps most common and use the most straightforward setup. The addition of servomotors for dynamic control of muscle length allows simulation of dynamic conditions (eccentric, isotonic, etc.) that may be modified by disease or other processes (22, 23). For in vitro studies, the muscle is anchored by ligating the tendon (origin) to a support, for in vivo studies, the bone (femur) is clamped to prevent movement. The other tendon (insertion) is then coupled to a force transducer. In both cases, a recording electrode is also placed in contact with the muscle to record the compound action potential, and a stimulating electrode is used to stimulate the nerve or the muscle, as described below. 

The sensitivity of force measurement is dependent on the distance between the force transducer and where the force occurs. Thus for force measurement, instrumentation of the punches is more advantageous than instrumentation of the machine frame. However, since punch and die sets have to be exchanged between different runs of the machines, instrumentation of the punch holder, the machine frame, or the roller pin is most widely spread. 

Yeh, C., Altaf, S. A., and Hoag, S. W. (1997), Theory of force transducer design optimization for die wall stress measurement during tablet compaction Optimization and validation of split-web die using finite element analysis, Pharm. Res., 14, 1161— 1170. 

Hoag, S. W., Nair, R., and Muller, F. X. (2000), Force-transducer-design optimization for the measurement of die-wall stress in a compaction simulator, Pharm. Pharmacol. Commun., 6(7), 293-298. 

The tensile force and birefringence were simultaneously measured as functions of the strain. In brief, the samples were suspended vertically between two clamps the lower clamp was fixed, and the upper clamp was connected to a force transducer (Statham strain gauge). The output of the transducer was monitored by a Hewlett-Packard chart recorder (7, 8). Values of the birefringence An were determined by using a single-frequency He-Ne laser according to well-established procedures (2, 7, 8). Values were calculated directly from the sample thickness and the relative retardation R, which was measured with a Babinet-type compensator. The measurements on the 660-21.3 X 10 samples were carried out at 0-90 °C, and those on the 880-21.3 X 10 samples were carried out at 25 °C. 

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