DayTronic 5M78 Manual - Página 8

Procurar online ou descarregar pdf Manual para Unidade de controlo DayTronic 5M78. DayTronic 5M78 16 páginas. Ac strain gage conditioner module

3 GENERAL DESCRIPTION AND CALIBRATION

The Model 5M78 is useful in applications involving tranformer coupling to the strain gage

bridge (for example, rotary transformer torque sensors) and in certain appications that require high

sensitivity with optimum signal-to-noise characteristics. Carrier amplifiers offer higher sensitivity

than dc amplifiers and, since they respond only to the modulated carrier frequency, they reject certain

extraneous voltages that can cause error in dc systems. These error sources include thermocouple

or galvanic voltages in the cable-connector system, homopolar voltages from rotating machinery,

low-frequency pickup, and 1/f noises of various origin.

Calibration of the 5M78 is accomplished by the conventional shunt technique, using an internally

(or externally) installed calibration resistor, or via the "dead-weight" method.

Calibration Resistor. If a fixed resistor is shunted across one arm of a strain

gage bridge, it produces an unbalance equivalent to that of a particular value of

mechanical input. If this Equivalent Input value is accurately known, it can be used

as a reference point for shunt calibration of the system. Upon completion of

installation of the transducer and its associated cabling, the user can:

(1)

Perform an overall dead weight calibration using a precisely known

value of mechanical input. The calibration can then be transferred to the

installed calibration resistor for convenience in subsequent checking.

(2)

Replace the installed calibration resistor with one (or an equivalent

resistance value) supplied by the transducer manufacturer to achieve a

precisely known Equivalent Input allowing the instrument sensitivity to

be adjusted correctly.

(3)

Determine the Equivalent Input value for the installed calibration resis-

tor, knowing the transducer sensitivity, and adjust the instrument sen-

sitivity accordingly.

A one percent 59-kilohm calibration resistor is installed in the 5M78 at the factory.

The installed resistor can usually be used even though the transducer calibration

data mentions some other resistance value. In Section 4 of this manual, the tech-

niques described above are demonstrated. If, however, the installed value of the

calibration resistor is not appropriate for the transducer and measurement range to

be used, the 59-kilohm resistor should be replaced at this time. The calibration

resistor is mounted on terminals located internally to the 5M78 conditioner's

printed-circuit board. It can be accessed by removing the instrument case (Fig. 5).

Note: A variety of Rotary Transformer Torque Transducers are supplied

with the appropriate calibration resistor integral to the transducer. When this type

of transducer is used it will be necessary to place a short across the 59-kilohm

resistor internal to the instrument. The transducer calibration resistor can be appropri-

ately connected to the 5M78 calibration circuit via the transducer cabling. Refer to

cabling diragam section of this manual in the area of CAL SENSE.

Calibration 5M78. 3