Pushrod transducer

If a double pushrod configuration is used, not only the expansion of the reference material must be added, but differences in length between sample and reference must be accounted for.4 If, for example, a one-inch sample and a 1/2-inch reference are used, then the expansion of 1/2-inch of reference and 1/2-inch of pushrod material must be added to the displacement indicated by the position transducer. When the sample and reference lengths are closely matched, the expansion of the pushrod... 

Another type of transducer is the pneumatic pressure transducer. It has good robustness, but poor temperature sensitivity, poor dynamic response, and average measurement error. The capillary transducer has fair robustness, fair temperature sensitivity, and fair dynamic response. The total measurement error varies from 0.5 to 3% depending on the quality of the transducer. The pushrod is similar to the capillary transducer, except that it tends to have poor temperature sensitivity and poor total error. The piezo-resistive transducer has good robustness because of its relatively thick diaphragm, good temperature sensitivity, good dynamic response, and low measurement error. A comparison of different pressure transducers is shown in Table 4.1. 

Weld configuration in capillary type (left) and pushrod type transducer... 

As a standard characterization the mean GTE (0/50) value in the temperature interval between 0 to 50 °G is measured in pushrod dilatometers made of titanium silicate (ULE 7971). An inductive transducer (LVDT) registers the motion of the pushrod with a resolution of 5 nm. The electromechanical sensitivity of the LVDT is calibrated with a Michelson interferometer. The expansivity of the dilatometer itself is determined by measuring standard materials for calibration. The standard materials (ULE , fused silica) have been measured especially for Schott in vacuum interferometers by the National Standardization Institutes PTB (Germany) and NPL (GB). 

---