Campbell CS225 Manuale delle Istruzioni Scaricare il pdf (Pagina 11)

CS225 Temperature String

TABLE 7-2. SGB3 Connection to Campbell Scientific Dataloggers

Colour

SGB3

Description

CR200(X)

CR800

CR1000

CR3000

CR5000

CR510

CR500

10(X)

CR23X

Red

L1 12V 12V

12V

Green

* Control Port

Control Port

Not Used

Black

G G G

Clear

* dedicated SDI-12 port on CR5000

To use more than one string per datalogger, you can either connect the different

strings to different SDI-12 compatible ports on the datalogger or change the

SDI-12 addresses of the strings and let them share the same connection. Using

the SDI-12 addressing method minimizes the use of ports on the datalogger

(see below for limits on the total cable length).

There are two ways to set the SDI-12 address of the CS225:

x By sending the required commands to the sensors via an SDI-12

recorder/datalogger that allows talk through to the sensor.

x By loading a program into the datalogger that sends the required

commands (see Section 7.5, Changing the SDI-12 Address Using

LoggerNet, and a Datalogger).

7.1.1 Long Cables

As the measurement data is transferred between the Temperature String and

datalogger digitally, there are no offset errors incurred with increasing cable

length as seen with analog sensors. However, with increasing cable length

there is still a point when the digital communications will break down,

resulting in either no response from the sensor or corrupted readings. The

original SDI-12 standard specifies the maximum total cable length for the cable

as being 61 meters (200 ft), but we are able to exceed this limit by:

x Using low capacitance, low resistance, screened cable.

x Ensuring that the power ground cable has low resistance and is connected

to the same ground reference as the datalogger control ports.

7.1.2 Power Conservation

The CS225 draws less than 1 mA of current per sensor between polling

sessions from its 12 V supply. In many applications this is minimal compared

to overall system power use, so the sensor can be permanently powered to

avoid the warm up period.

In very low power applications battery power can be conserved by turning the

12 V supply to the CS225 on a minimum of 10 seconds before the CS225 is

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Campbell CS225 Manuale delle Istruzioni Pagina 11

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