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ROOTS
®
Model 5 Prover Software Manual
Appendix
B. TC Unit Operational Check
This procedure may be used to verify the overall accuracy of the TC Unit, independent of the basic meter
body measurement accuracy. The designed accuracy for the TC Unit is within ± 0.5% of the theoretical
correction for gas temperatures between -20°F to +120°F (-29°C and +49°C).
All Series B3 ROOTS TC meters are compensated to a 60° F (15° C) Base Temperature.
The TC Unit Operational Check is based upon Calculated Measurement Counts (actual measurement) versus
Theoretical Counts, using a 25 cycle count of the compensation cycle. This is the best method for determin-
ing the accuracy of the TC unit with the meter in service. By using the 25 cycle method, all of the gears in
the TC unit make a complete revolution, and thus provides a greater amount of confidence in the resulting
accuracy calculation. The method for determining the theoretical counts for a 25 cycle test is outlined in the
“Calculating Theoretical Counts” section.
A ROOTS
®
Transfer Prover is a commonly used device for conducting a TC Unit Operation Check in the shop
or when the meter is not in service. The prover is used for flow rate control and indication of temperature
during the test procedure. The prover may also be used during this time to test the accuracy of the basic
meter body using the non-compensated odometer or the RPM test wheel. The information derived from
the TC Unit Operation Check is then combined with the meter’s non-compensated accuracy to determine the
meter’s overall accuracy, including temperature compensation (basic meter body non-compensated accuracy
X accuracy of TC unit = overall or combined accuracy).
Procedure for the TC Unit Operational Check
1. Measure and record stabilized gas (or air) temperature directly at the meter inlet using a certified
temperature standard.
Inaccurate results may occur if the gas temperature is not stabilized before starting the test.
2. Record the temperature displayed by the Accessory Unit’s temperature probe. The indicated
temperature is visible through the accessory housing window located above the odometers.
Compare to the readings taken in step 1. Both values should agree within ± 4 °F.
The temperature indicated by the unit’s temperature probe will not be used since this is an
estimated reading. Use the temperature recorded in Step 1 as the reference temperature for the
TC unit operational check.
3. Observe the Temperature Compensated volume odometer. When the odometer stops turning
after an intermittent compensating cycle, record the last 3-digit reading (Ci) indicated on the
odometer, PLUS the value indicated by the graduated marks on the test wheel. Read as a whole
number. (See the Sample Counter Reading in Figure 13 below.)
Some of these digits may be partially or completely obscured by masking. The masking must be
removed if the readings are not visible.
Figure 13
: A reading of 9756 would be the number recorded for TC unit operational check.
