26
Installation
2. Set the full-scale counts in the Analog section. The instrument default is 1000 for all
four channels. Each channel can be individually set and is independent of the other.
The analog outputs are updated at the end of each sample period. When an
instrument is first powered on, all outputs are set to 4 milliamps.
The expected analog output voltage across the load resistor as related to the channel
count can be found from equation (1):
(1)
where:
SC = Sample Count value at the end of the sample period
FC = Full-scale channel Count
RL = value of the Load Resistor in ohms
The expected output voltage when the full-scale channel count is 1000 with a 100, 250
and 500-ohm resistor is shown in Table 7.
Note: A fault condition for Flow or sensor Cal Fail results in a value close to 0 volts (< 2 mA).
Note: Count Alarms that are set in the Setup Utility work only with the utility and cannot be used as
an LED indicator or current loop output.
3.6.10 Testing Analog Output
3.6.10.1 Channel Scaling Test
1. If the instrument uses the flow monitoring option, make sure that the central vacuum
is connected and is operating correctly.
2. Connect the unit to the data acquisition system load resistors.
Note: As an option, use a set of load resistors with 0.1% accuracy and at least 0.25 W
capability. Values of 100, 250 or 600 ohms are typically used.
Table 7 Output voltage with 100, 250 and 500-ohm resistors
1
1
A full-scale channel count (FC) of 1000 was used to calculate each voltage.
Output voltages (±0.01) V
Sample Count RL = 100 Ω RL = 250 Ω RL = 500 Ω
0 0.40 V 1.00 V 2.00 V
100 0.56 V 1.40 V 2.80 V
200 0.72 V 1.80 V 3.60 V
300 0.88 V 2.20 V 4.40 V
400 1.04 V 2.60 V 5.20 V
500 1.20 V 3.00 V 6.00 V
600 1.36 V 3.40 V 6.80 V
700 1.52 V 3.80 V 7.60 V
800 1.68 V 4.20 V 8.40 V
900 1.84 V 4.60 V 9.20 V
1000 2.00 V 5.00 V 10.00 V
SC()FC()⁄ 16×〈〉4+
1000
---------------------------------------------------------- -
RL× output voltage across load resistor=
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