Milanodan
06-22-2010, 01:18 PM
Decided to try my old Pact "Precision" chronograph one more time before I bought a different brand. It's been erratic lately, only "seeing" about 25% of the shots.
Started by calling Pact. Guy who answered the phone said he could help with tech. questions. Asked him if there were any checks I could do at home to figure out what was wrong. Told me nothing can be done on the chrono. itself except to send it in, where they check it on a "$10,000 machine".
Then he told me I could check the sensors with a VOM. Ah, should I expect milli or microvolt readings? Nope, they work via resistance. OK, how many ohms should I expect. "I don't know--they work on changes in resistance." OK, does the resistance get higher or lower as the light increases? "I don't know".
Armed with all this new info (right), I started checking resistances vs amount of light. After several screwy readings, I discovered the NEGATIVE lead of the meter must be connected to the TIP of the phone plug. I found infinite resistance at low light, decreasing rapidly as the light was increased. Under a 9 AM pure blue sky day here in Arizona, I got ~63,000 ohms--without anything over the sensors/Skyscreens.
After taping a very thin piece of translucent plastic shopping bag ~6" above the sensor, the reading dropped to ~28,000 ohms, verifying that a blue sky is actually fairly dark.
Fired a few shots from my low power air rifle over the sensors with the plastic above them. Got readings every time as long as the pellet passed over the sensor by at least ~4-5". Got no readings if the pellet was too close to the sensor--was probably off to one side a bit.
Lesson learned--keep the shots high and use thin white/translucent plastic over the sensors.
Started by calling Pact. Guy who answered the phone said he could help with tech. questions. Asked him if there were any checks I could do at home to figure out what was wrong. Told me nothing can be done on the chrono. itself except to send it in, where they check it on a "$10,000 machine".
Then he told me I could check the sensors with a VOM. Ah, should I expect milli or microvolt readings? Nope, they work via resistance. OK, how many ohms should I expect. "I don't know--they work on changes in resistance." OK, does the resistance get higher or lower as the light increases? "I don't know".
Armed with all this new info (right), I started checking resistances vs amount of light. After several screwy readings, I discovered the NEGATIVE lead of the meter must be connected to the TIP of the phone plug. I found infinite resistance at low light, decreasing rapidly as the light was increased. Under a 9 AM pure blue sky day here in Arizona, I got ~63,000 ohms--without anything over the sensors/Skyscreens.
After taping a very thin piece of translucent plastic shopping bag ~6" above the sensor, the reading dropped to ~28,000 ohms, verifying that a blue sky is actually fairly dark.
Fired a few shots from my low power air rifle over the sensors with the plastic above them. Got readings every time as long as the pellet passed over the sensor by at least ~4-5". Got no readings if the pellet was too close to the sensor--was probably off to one side a bit.
Lesson learned--keep the shots high and use thin white/translucent plastic over the sensors.