Campbell Scientific CR5000 Measurement and Control Module - Manual (Page 30)

Section 1. Installation and Maintenance
1-6
1.6.2 CR5000 with Low Profile Base (No Battery)
If a CR5000 without batteries is to be powered from the 12 Volts of a motor
vehicle, a second 12 V supply is required. When the starting motor of a
vehicle with a 12 V electrical system is engaged, the voltage drops
considerably below 11 V, which would cause the CR5000 to stop measurement
every time the vehicle is started. The second 12 V supply prevents this
malfunction. Figure 1.6-3 shows connecting the two supplies to a CR5000
without a battery base. The diodes allows the vehicle to power the CR5000
without the second supply attempting to power the vehicle.
CR5000
Panel
+12V
G
FIGURE 1.6-3. Connecting CR5000 without Battery Base to Vehicle
Power Supply
1.7 CR5000 GROUNDING
Grounding of the CR5000 and its peripheral devices and sensors is critical in
all applications. Proper grounding will ensure the maximum ESD
(electrostatic discharge) protection and higher measurement accuracy.
1.7.1 ESD Protection
An ESD (electrostatic discharge) can originate from several sources. However,
the most common, and by far potentially the most destructive, are primary and
secondary lightning strikes. Primary lightning strikes hit the datalogger or
sensors directly. Secondary strikes induce a voltage in power lines or sensor
wires.
The primary devices for protection against ESD are gas-discharge tubes
(GDT). All critical inputs and outputs on the CR5000 are protected with GDTs
or transient voltage suppression diodes. The GDTs fire at 150 V to allow
current to be diverted to the earth ground lug. To be effective, the earth
ground lug must be properly connected to earth (chassis) ground. As shown in
Figure 1.7-1, the power ground and signal ground are independent lines until
joined inside the CR5000.