Campbell Scientific CR800 and CR850 Measurement and Control Systems - Manual (Page 187)

Section 7. Installation
187
Example:
Probe: Water Content
Power Usage:
• Quiescent: 0.25 mA
• Measurement: 120 mA
• Measurement Time: 15 s
• Active: 66 mA
• Timeout: 15 s
Probes 1, 2, 3, and 4 are connected to SDI-12 / Control Port 1.
The time line in table Example Power Usage Profile for a Network of SDI-12
Probes
(p. 187)
shows a 35-second power-usage profile example.
For most applications, total power usage of 318 mA for 15 seconds is not
excessive, but if 16 probes were wired to the same SDI-12 port, the resulting
power draw would be excessive. Spreading sensors over several SDI-12 terminals
will help reduce power consumption.
Table 28. Example Power Usage Profile for a Network of SDI-12 Probes
Sec Command
All
Probes
Awake
Time
Out
Expires 1 mA 2 mA 3 mA 4 mA
Total
mA
1 1M! Yes 120 66 66 66 318
2 120 66 66 66 318
• • • • • •
• • • • • •
• • • • • •
14 120 66 66 66 318
15 Yes 120 66 66 66 318
16 1D0! Yes 66 66 66 66 264
17 66 66 66 66 264
• • • • • •
• • • • • •
• • • • • •
29 66 66 66 66 264
30 Yes 66 66 66 66 264
31 0.25 0.25 0.25 0.25 1
• • • • • •
• • • • • •
• • • • • •
35 0.25 0.25 0.25 0.25 1