Section 7. Installation
terminals provides protection from intermittent high voltages by clamping these
transients to within the range of 19 to 21 V. Sustained input voltages in excess of
19 V, can damage the TVS diode.
7.2.2 Calculating Power Consumption
System operating time for batteries can be determined by dividing the battery
capacity (ampere-hours) by the average system current drain (amperes). The
CR800 typically has a quiescent current drain of 0.5 mA (with display off) 0.6
mA with a 1 Hz sample rate, and >10 mA with a 100 Hz scan rate. When the
CR1000KD Keyboard/Display is active, an additional 7 mA is added to the
current drain while enabling the backlight for the display adds 100 mA.
7.2.3 Power Sources
Related Topics:
• Power Input Terminals — Specifications
• Power Supplies — Quickstart
(p. 37)
• Power Supplies — Overview (p. 83)
• Power Supplies — Details (p. 94)
• Power Supplies — Products (p. 576)
• Power Sources (p. 95)
• Troubleshooting — Power Supplies (p. 477)
Be aware that some Vac-to-Vdc power converters produce switching noise or ac
(p. 489)
ripple as an artifact of the ac-to-dc rectification process. Excessive
switching noise on the output side of a power supply can increase measurement
noise, and so increase measurement error. Noise from grid or mains power also
may be transmitted through the transformer, or induced electro-magnetically from
nearby motors, heaters, or power lines.
High-quality power regulators typically reduce noise due to power regulation.
Using the optional 50 Hz or 60 Hz rejection arguments for CRBasic analog input
measurement instructions (see Measurements — Details
(p. 311)) often improves
rejection of noise sourced from power mains. The CRBasic standard deviation
instruction, SDEV(), can be used to evaluate measurement noise.
The main power for the CR800 is provided by an external-power supply.
7.2.3.1 Vehicle Power Connections
If a CR800 is powered by a motor-vehicle power supply, a second power supply
may be needed. When starting the motor of the vehicle, battery voltage often
drops below the voltage required for CR800 operation. This may cause the CR800
to stop measurements until the voltage again equals or exceeds the lower limit. A
second supply can be provided to prevent measurement lapses during vehicle
starting. The figure Connecting to Vehicle Power Supply
(p. 96) illustrates how a
second power supply is connected to the CR800. The diode OR connection causes
the supply with the largest voltage to power the CR800 and prevents the second
backup supply from attempting to power the vehicle.
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