DigitalFlow™ Multipurpose Ultrasonic Liquid Flowmeter Service Manual 5
Chapter 1. Calibration
1.4 Calibrating the Analog Inputs
Analog inputs may be added to the Model DF868 flowmeter by installing an Analog Inputs Option Card in one (or
more) of the six expansion slots. The option card contains two analog inputs, which are designated as A and B. Each of
the inputs must be calibrated at both the zero-point and full-scale values. After calibrating the inputs, their linearity
should be tested.
Calibration of the analog inputs requires the use of a calibrated current source. If an independent calibrated current
source is not available, one of the
Slot 0 analog outputs may be used for the calibration. During the analog input
calibration, the Slot 0 analog output will supply the low reference, high reference, 4 mA and 20 mA signals at the
appropriate times.
Note: If a
Slot 0 analog output will be used to calibrate the analog inputs, make sure that the Slot 0 analog output
calibration procedure has already been completed.
Connect the
Slot X analog output(s) (or an independent calibrated current source) to the analog input(s) on the option
card, as shown in Figure 3 below. Refer to the menu map in Figure 6 on page 13 as a guide.
Figure 3: Analog Input Calibration Connections
For this discussion, assume that the option card has been installed in
Slot x.
Note: The zero point of the analog input may be set for either 0 mA or 4 mA. However, the calibration procedure
always uses the 4 mA point, as the meter will extrapolate this value to obtain the 0 mA point.
Analog Input Option Card
A
INLO
A
RTN
A
+24V
A
INHI
8
1
B
INLO
B
RTN
B
+24
B
INHI
B
RTN
B
SIG
A
RTN
A
SIG
Terminal Block I/O (Slot 0)
41
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