Measurement Computing DBK Part 2 - Manual (Page 183)

DBK Option Cards and Module 907492 DBK90 pg. 9
Vehicle Testing and Noise Reduction
Power Connections and Analog Common
To properly measure vehicle-attached thermocouples differentially, it is necessary to have an analog common
connection to the negative side of the vehicle’s electrical system. A jack labeled ACOM, located on the DBK90’s
mini-TC panel, provides a connection point for analog common. If analog common is not connected, true
differential readings cannot be obtained due to noise. For this reason, the chassis of the primary data acquisition
device, e.g., DaqBook/2000A, must also have a good connection to the negative side of the vehicle’s electrical
system.
All grounds should come together at the negative terminal of the test vehicle’s battery. Connecting the grounds at
any other point may introduce noise. One line, with a 2mm banana plug is used to connect the battery’s negative
terminal to the DBK90’s ACOM jack. The ACOM jack connects internally to the DBK90’s P1, pin # 28 (AGND).
Connections for a Vehicle Test
Note 1: The ACOM connector is a 2mm banana jack. To ensure a good connection that will not
damage the jack, use a Pomona® Electronics 2mm banana plug (p/n 5936-0). The use
of a different plug (including a 0.08 inch tip type) may damage the ACOM jack.
Note 2: It is best to use a male DIN5 connector to connect the lines from the battery to the
DaqBook/2000’s female DIN5 connector. A Switchcraft® male DIN5 Connector
(p/n 12BL5M) can be used for making your own cable.
The lines that will connect to the vehicle battery are soldered to the male DIN5 connector. As indicated in the first
figure on this page, the +V
IN
line connects to the battery’s positive (+) terminal and should have a 7.5 amp fuse in
series with the line. The -V
IN
and Chassis Ground lines both connect to the battery’s negative terminal.