78
CLCH-SVX03C-EN
Startup
VCM (Transducer) Calibration.
The VCM has an auto-zero function that recalibrates the
transducer once every minute. When troubleshooting, allow for the recalibration time before
making any measurements.
Input Power.
The only input the VCM needs is the 24 Vac power connected to terminals 1TB1–5
and 1TB1–6.
Output Velocity Signal.
The 2 to 10 Vdc linear output signal from the VCM represents air
velocity. This voltage can be converted to represent airflow (cfm or L/s) using the formula below,
Table 17
and
Table 18
.
In
Table 18
the cfm at 10Vdc is a calculated value based on area and peak velocity. In certain
situations, it can be advantageous to raise the velocity of air through the remaining Traq dampers
by closing off one or more dampers in the unit. The cfm at 10Vdc can be recalculated based on the
proportion of remaining Traq dampers or by multiplying the remaining area of dampers by peak
velocity.
Table 17. Altitude adjustment factors
Airflow = k (cfm @ 10V)
or
Airflow = k (L/s @ 10V)
For example, if the VCM on a size 30 M-Series air handler at sea level
(k=1) has a 10-volt signal, it would represent 18,376 cfm (8672 L/
s) through the Traq damper. If the voltage were 6 volts, airflow
through the Traq damper would be 9,188 cfm (3,930 L/s).
Sea level = 1.0
Elevation (feet)
k
1000
0.982
2000
0.964
3000
0.949
4000
0.930
5000
0.914
6000
0.897
7000
0.876
8000
0.860
9000
0.846
10,000
0.825
volts 2
–
(
)
8
------------------------------
volts 2
–
(
)
8
------------------------------
Table 18. Back or Top Inlet Traq Dampers - Air-Mixing and Economizer Section - VCM voltage versus airflow at sea level
Unit
Size
Part
Number
Traq Damper
Size (inches)
Quantity
Total Area
ft
2
Peak Velocity
(fpm)
CFM@10VDC
Peak Velocity
L/s@10VDC
03
DMP01123
13
1
0.9213
2500
2303
1087
06
2
1.8426
4606
2174
08
10
3
2.7639
6910
3261
12
DMP01124
16
3
4.1867
2650
11095
5236
14
17
21
DMP01125
24
2
6.2800
2700
16956
8002
25
30
DMP01663
20
3
6.5417
2650
17335
8181
35
DMP01125
24
3
9.4200
2700
25434
12004
40
50
DMP01126
28
3
12.8217
2700
34619
16338
57
66
4
17.0956
46158
21784
80
5
21.3694
57698
27230
100
6
25.6433
69237
32676
120