Usp Limits - Signet 9900 Operating Instructions Manual

USP Limits

USP (United States Pharmacopoeia) has defi ned a set of conductivity values (limits)
to be used for pharmaceutical water. The standard requires that conductivity
measurement without temperature compensation be used for these applications.
The limits vary according to the temperature of the sample. The 9900 has the USP
limits stored in memory. It will automatically determine the proper USP limit based
on the measured temperature.
Using the USP function
USP setpoints are defi ned as a percentage below the USP limit, so a USP alarm
is always a HIGH alarm. The 9900 can be set to warn you if the conductivity
approaches within a set percentage of the USP limit.
The following settings and conditions are required for a USP relay function:
1. In the RELAY menu:
• RELAY MODE must be set to USP.
2. In the INPUT menu:
• COND UNITS must be set to μS.
• TEMP COMP must be set to None.
Example:
• The water temperature is 19 ºC, so the USP limit is 1.0 μS.
• The USP PERCNT is set to 40%.
• The relay will be activated when the conductivity value reaches 40% below the
1.0 USP limit, or 0.6 μS.
• If the water temperature drifts to more than 20 ºC, the 9900 will automatically
adjust the USP limit to 1.1. The relay will now be activated when the
conductivity value reaches 40% below 1.1 μS (0.66 μS).
Temperature USP limit
Range (ºC) (μS)
0 to < 5 0.6
5 to < 10 0.8
10 to < 15 0.9
15 to < 20 1.0
20 to < 25 1.1
25 to < 30 1.3
30 to < 35 1.4
35 to < 40 1.5
40 to < 45 1.7
45 to < 50 1.8
50 to < 55 1.9
55 to < 60 2.1
60 to < 65 2.2
65 to < 70 2.4
70 to < 75 2.5
75 to < 80 2.7
80 to < 85 2.7
85 to < 90 2.7
90 to < 95 2.7
95 to < 100 2.9
100 to < 105 3.1
9900 Transmitter 63