Campbell-scientific CR800 and CR850 Measurement and Control Systems Instrukcja Użytkownika Pobierz pdf (Strona 297)

100

101

Section 8. Operation

297

Table 63. StrainCalc() Instruction Equations

StrainCalc()

BrConfig Code

Configuration

Full-bridge strain gage. Half the bridge has two gages parallel to +

and

, and the other half to - and + :

where:

•

: Poisson's Ratio (0 if not applicable)

• GF: Gage Factor

• V

: 0.001 (Source-Zero) if BRConfig code is positive (+)

• V

: -0.001 (Source-Zero) if BRConfig code is negative (-)

and where:

• "source": the result of the full-Wheatstone-bridge measurement (X = 1000 *

/ V

) when multiplier = 1 and offset = 0.

• "zero": gage offset to establish an arbitrary zero (see FieldCalStrain() in

FieldCal() Demonstration Programs

(p. 154) ).

StrainCalc Example: See FieldCalStrain() Demonstration Program

(p. 162)

8.1.4 Thermocouple

Thermocouples are easy to use with the CR800. They are also inexpensive.

However, even though the Quickstart Tutorial

(p. 33) uses a thermocouple as an

exercise in measurement, the CR800 is not designed for accurate thermocouple

measurements when thermocouples are attached directly to the CR800 wiring

panel. The lack of an insulating wiring terminal cover and the nature of the

plastic encasement will probably induce significant error in the reference junction

temperature measurement. If an external reference junction is to be used,

Campbell Scientific strongly encourages users to carefully evaluate relevant

parts of the Thermocouple Measurements section of the CR1000 Datalogger

Operator's Manual, which is available at www.campbellsci.com.

8.1.5 Pulse

Figure Pulse-Sensor Output Signal Types (p. 39) illustrates pulse input types

measured by the CR800. Figure Switch-Closure Pulse Sensor

(p. 298) is a

generalized schematic showing connection of a pulse sensor to the CR800. The

CR800 features two dedicated pulse-input channels, P1 through P2, and four

digital I/O channels, C1 through C4, for measuring frequency or pulse output

sensors.

As shown in table Pulse-Input Channels and Measurements

(p. 39), all CR800

pulse-input channels can be measured with CRBasic instruction PulseCount().

PulseCount() has various parameters to customize it to specific applications.

Digital I/O ports C1 through C4 can also be measured with the TimerIO()

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