©Kendrick Astro Instruments – DigiFire FX-Pro Dew Controller User Guide 05 FEB 2019 Page 4of 6
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On a refractor or SCT, the sensor is placed under the Dew Heater. So, attach your dew heater and then slide the sensor underneath so the aluminum rivet
is touching the optical tube.
Heater Ports 1 and 2 (the bottom ports) are capable of using either Duty-Cycle OR Temperature Sensing to control heater output. The Temperature Sensing
feature works by knowing the current temperature of the ambient (outside) air AND the current temperature of your telescope OTA. Then you simply
“program” the unit to maintain the temperature “offset” of your optics to be xx°C (0.5 – 10.0) above ambient air temperature. If outside air temperature
falls, the DigiFire will allow the optics temperature to fall, but will always maintain the temperature “offset”. The objective is to keep the optics to 2°C
above ambient. It doesn’t matter how warm/cold it is outdoors, what counts is keeping the optics warmer than the outside air.
On most telescopes, the sensor cannot measure the actual temperature of the mirror/lens directly. The goal is to allow the heater to turn ON when the
mirror/lens is within a few degrees of outside air temperature to prevent water vapor from condensing onto cold glass. For most telescope owners, the
dew heater attaches to the Optical Tube as close as possible to where the lens or mirror is located. Heat seeks the easiest path (the coldest point) and will
transfer into the glass optics. The DigiFire FX-Pro Controller can be set to maintain OTA temperature at a constant temperature above ambient air
temperature (between 0-10°C above ambient).
Are Port Lights 1 and/or 2 Blinking? If port lights are blinking, it means:
-Unit is programmed to use Temperature Regulation.
-1 or more sensors are NOT present or malfunctioning.
The unit needs an Ambient AND Optic Temperature Sensor to function. The lights blink to tell you that you have programmed
it to maintain a temperature, but it can’t do that unless both sensors are available. If you have both Ports 1 and 2
programmed to use temperature regulation, the light will blink if the Ambient Sensor and/or either/both Port Sensors is
missing. When a required Sensor is missing, the unit will revert to Duty-Cycle regulation, but the lights will continue to blink
until a sensor is plugged in OR temperature regulation is turned OFF (set to 0.0). The display will also show “n/c” (not
connected) when 1 or more sensors is absent and the display will also show the duty-cycle setting it has defaulted to.
TIPS for temperature settings:
Every telescope is unique and finding the ideal temperature setting for your telescope will require some simple testing.
-On most telescopes, dew heaters are on the outside edges of your OTA and some heat will escape before reaching the center of your lens/mirror.
That means the center will be cooler than what is measured by the sensor. Logic dictates that the OTA will be warmer than the center and the
temperature “offset” will need to be raised to ensure the center of the optics will be 1-2 degrees above ambient.
-There are no published “recommended settings” because there are just too many variables:
oA Dew Shield will help the dew heater do its job using less heat
oSize of lens/mirror changes how far heat applied to the outside needs to travel before reaching the center.
oGenerally, the larger the optics, the higher the temperature differential will need to be. Experimentation will reveal the ideal setting for
your equipment. For example, start at a fairly high differential and then gradually reduce until you begin to show signs of dew
formation. Allow at least 30-45 minutes for temperatures to equalize before attempting a new setting. Do this over several nights.
oExcess heat will degrade images, so it is worth the effort to experiment with finding “how low can you go”.
-Suggested starting points:
oLarge SCT (11”-16”): 8°
oSmall SCT (6”-8”): 6°
oSmall/midsize refractor (60mm-110mm): 4°
oLarge refractor (≥110mm and above): 6°
-Brand of heater makes a difference. For best results, use Kendrick Premier Brand which produce considerably more heat than any other brand
(including our own FireFly Brand). Some heaters just can’t get hot enough to maintain desired temperature. Watts spec for heaters is directly
related to how much heat they can produce, regardless of the amount of power applied.
The DigiFire FX-Pro supports Temperature Sensing on 2 telescopes at the same time. This means that there would be 3 sensors in use: 1 is for Ambient Air
Temperature, 2 & 3 are for telescope optics. The Ambient and Optics temperature sensors are identical, and no calibration is required.
NOTE: Sensor Calibration is based on the “audio cables” supplied by Kendrick. Cables purchased elsewhere, or modified
(lengthening/shortening), may alter sensor calibration.
Typical Temperature Differential Settings: Every telescope is different, so there is no “one-setting-fits-all”. The aperture of your optics will play a major role
in determining what is best for your equipment. Using a Dew Shield will also help reduce the amount of heat that is needed to keep optics free of dew &
frost. Excess heat will reveal “turbulence” and will also drain your battery faster, so we urge you experiment to find the ideal temperature differential for
each of your telescopes.
•For small refractors, try starting with 4° differential and then lower by 0.5°-1° until you start to see signs of dew/frost.
•For SCT telescopes, try starting with a 8° differential and lower by 0.5°-1° until you start to see signs of dew/frost.
NOTE: 1 Ambient and 1 Optic Sensor was included with the purchase of your DigiFire FX-PRO Controller. If you wish to use Temperature Sensing on a 2nd
telescope, you will need to purchase an additional temperature sensor (SKU: 2001-12-SCBL6).
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