Does This Behaviour Indicate Bad pH Probe?

[Kengar]

I posted last night re calibration technique. I let new probe take FOREVER to settle before hitting select in 7.0 then 10.0 buffer. Some of the readings today seem suspicious (pH of 8.5). Here is printout showing response while in RUN mode when dropping the probe into 7.0 for two and half hours then moving it over to 10.0. Note that it never reached 7.0 and was still dropping after 2.5 hours. Does this behaviour suggest bad probe? I think it does.

Here's the datalog. Note that I eventually dropped the probe back into the tank, which is reflected here but not in the graph above.

Date Temp pH ORP
18:15 10/04/2009 79.2 8.50 122
18:18 10/04/2009 79.1 8.50 123
18:21 10/04/2009 79.1 8.50 124
18:24 10/04/2009 79.0 8.47 126
18:27 10/04/2009 79.0 8.47 128
18:30 10/04/2009 79.0 8.46 129
18:33 10/04/2009 79.0 8.45 117
18:36 10/04/2009 79.0 8.45 116
18:39 10/04/2009 78.9 8.43 116
18:42 10/04/2009 79.0 8.43 120
18:45 10/04/2009 79.0 8.43 120
18:48 10/04/2009 79.0 8.43 121
18:51 10/04/2009 79.0 8.43 122
18:54 10/04/2009 79.1 8.43 123
18:57 10/04/2009 79.1 8.43 124
19:00 10/04/2009 79.1 8.43 126
19:03 10/04/2009 79.1 8.43 127
19:06 10/04/2009 79.1 8.43 128
19:09 10/04/2009 79.1 8.42 130
19:12 10/04/2009 79.1 8.42 131
19:15 10/04/2009 79.1 8.41 132
19:18 10/04/2009 79.1 8.41 133
19:21 10/04/2009 79.1 8.40 135
19:24 10/04/2009 79.1 8.40 138
19:27 10/04/2009 79.1 8.40 139
19:30 10/04/2009 79.1 8.39 139
19:33 10/04/2009 79.1 8.39 139
19:36 10/04/2009 79.1 8.39 129
19:39 10/04/2009 79.0 8.38 128
19:42 10/04/2009 79.0 8.38 130
19:45 10/04/2009 79.0 8.38 132
19:48 10/04/2009 79.0 8.37 133
19:51 10/04/2009 79.0 8.37 135
19:54 10/04/2009 79.0 8.37 136
19:57 10/04/2009 79.0 8.36 137
20:00 10/04/2009 79.0 8.36 134
20:03 10/04/2009 79.0 7.84 097
20:06 10/04/2009 79.0 7.69 089
20:09 10/04/2009 79.0 7.61 088
20:12 10/04/2009 79.0 7.54 090
20:15 10/04/2009 78.9 7.50 092
20:18 10/04/2009 78.9 7.46 095
20:21 10/04/2009 78.9 7.43 098
20:24 10/04/2009 78.9 7.41 100
20:27 10/04/2009 78.9 7.40 102
20:30 10/04/2009 78.9 7.38 106
20:33 10/04/2009 78.9 7.36 108
20:36 10/04/2009 78.9 7.35 108
20:39 10/04/2009 78.8 7.34 105
20:42 10/04/2009 78.8 7.33 101
20:45 10/04/2009 78.9 7.32 098
20:48 10/04/2009 78.9 7.32 098
20:51 10/04/2009 79.0 7.31 102
20:54 10/04/2009 79.0 7.31 105
20:57 10/04/2009 79.0 7.30 107
21:00 10/04/2009 79.0 7.30 103
21:03 10/04/2009 79.0 7.29 105
21:06 10/04/2009 79.0 7.29 106
21:09 10/04/2009 79.0 7.28 108
21:12 10/04/2009 79.0 7.28 109
21:15 10/04/2009 78.9 7.28 105
21:18 10/04/2009 78.9 7.27 091
21:21 10/04/2009 78.9 7.27 091
21:24 10/04/2009 78.9 7.27 093
21:27 10/04/2009 78.9 8.07 093
21:30 10/04/2009 78.8 9.18 093
21:33 10/04/2009 78.8 9.46 098
21:36 10/04/2009 78.9 9.63 100
21:39 10/04/2009 78.9 9.74 102
21:42 10/04/2009 79.0 9.80 104
21:45 10/04/2009 79.0 9.87 106
21:48 10/04/2009 79.0 9.91 106
21:51 10/04/2009 79.0 9.95 107
21:54 10/04/2009 79.0 9.97 108
21:57 10/04/2009 78.9 10.0 109
22:00 10/04/2009 78.9 10.0 111
22:03 10/04/2009 78.9 10.0 109
22:06 10/04/2009 78.9 8.98 156
22:09 10/04/2009 78.9 8.52 153
22:12 10/04/2009 78.8 8.40 155
22:15 10/04/2009 78.8 8.35 157
22:18 10/04/2009 78.9 8.31 159
22:21 10/04/2009 78.9 8.29 148
22:24 10/04/2009 79.0 8.27 140
22:27 10/04/2009 79.0 8.26 136
22:30 10/04/2009 79.1 8.25 136
22:33 10/04/2009 79.1 8.25 140
22:36 10/04/2009 79.1 8.24 143
22:39 10/04/2009 79.0 8.23 146
22:42 10/04/2009 79.0 8.22 147

 

[Los]

Do your lights turn off at 8pm? It looks like there may be some interference. Both ORP and pH took a big jump then.

 

[Kengar]

i had the graph posted originally but deleted it from Photobucket, so no more image here. The jumps are when I put the probe in calibration solutions. Probe was clearly bad and is being exchanged.