Specifications

Section 1. Installation and Maintenance
1-11
1.6 Vehicle Power Supply Connections
If a CR3000 is 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 CR3000 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 CR3000. The diodes allows the vehicle to power the
CR3000 without the second supply attempting to power the vehicle.
CR3000
Panel
+12V
G
FIGURE 1.6-1. Connecting CR3000 to Vehicle Power Supply
1.7 CR3000 Grounding
Grounding the CR3000 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 CR3000 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 CR3000.