I am now having a problem getting a mass calibration on my Delta-S. After I
recovered from the down turbo pump and leak in the inlet valve, I discovered
that the peaks for my reference gas had shifted. I ran a mass calibration
with CO2 , the AMASS, BMASS and CMASS values were different from the
previous calibration but appear to be reasonable. When I went to instrument
control and CO2 cup configuration I still had no signal. I have done this a
few times now and this is what happens.
1. The instrument does a calibration scan, finds the reference mass
peaks at bdac of 3400-3600 for mass 12, bdac 7500-7800 for mass 28 and bdac
10600- 10800 for mass 44.
2. Then it goes to each peak and centers three times. The Bdacmid values
vary by 20 -30 bdac units and always start high and decrease.
3. The mass calibration is then calculated. The BDAC value for the CO2
cup configuration is always about 100 units less than the Bdacmid value for
4. If I do a BDAC scan, I find the peaks at a value close to the Bdacmid
value for mass 44. This is about 0.5 mass units higher than the cup
After talking to Frank Trensch at Finnigan, I have turned the Delta-S
completely off then back on to reset the electronics and have rebooted the
computer. But the same thing happens again.
I have made these observations but am at a loss to explain them or to
correct them. Sorry for the length of this post. Any ideas would be
Patrick D. Anderson
University of Wisconsin-Milwaukee
Great Lakes WATER Institute
600 E. Greenfield Ave
Milwaukee, WI 53204
Phone (414) 382-1731
Fax (414) 382-1705