Retrotec DM-2 - Manual (Page 23)

Page 23 of 72
©Retrotec Inc. 2012
If the test pressure (20 in this case) is close to the desired reference pressure (25 Pa in this case), then
the correction is small and the value of n does not play as large a role. However, if the test pressure is
much higher or lower than the reference pressure, the error can be greater.
The @ Pressure feature is very useful for ensuring that results taken when the pressure was not
adjusted perfectly are still accurate.
To continue the above example: The flow at 20 Pa is 100 CFM. Actual n is 0.7, but this is unknown.
Instead, 0.6 will be used.
The gauge would calculate:
𝐹𝑙𝑜𝑤@25 𝑃𝑎 =
25 𝑛 × 𝐶𝐹𝑀
20 𝑛
𝐹𝑙𝑜𝑤@25 𝑃𝑎 =
25 0.6 × 100
20 0.6
𝐹𝑙𝑜𝑤@25 𝑃𝑎 = 114 𝐶𝐹𝑀
However, if it was known that n was 0.7, the flow at 25 should have been:
𝐹𝑙𝑜𝑤@25 𝑃𝑎 =
25 0.7 × 100
20 0.7
𝐹𝑙𝑜𝑤@25 𝑃𝑎 = 117 𝐶𝐹𝑀
This value is less than 3% off from what it should be. If the test pressure was within 1 or 2 Pa of the
reference pressure of 25 Pa, the @ Pressure reading would be exact.
To change the n value
1. Press [Setup] to access the “Setup” menu.
2. Press [
 ] or [  ] to select "n" in the list. Press [Enter].
3. Input the new value between 0.5 and 1. Press [Enter].
3.1.7 Power Down Hour
The Power Down Hour helps to maximize battery power by enabling the DM-2 to automatically turn off
when it has been inactive for a set time period. The feature can be set to any value between 0 and 255
hours. Applying a 0 value will disable the Power Down feature, and the DM-2 will never automatically
shut down.
To change the Power Down Hour
1. Press [Setup] to access the Setup menu.
2. Press [

] or [

] to select "Power Down Hour" in the list. Press [Enter].