Oval Gear flowmeter Error Calculation and Adjustment
1.Flowmeter’s basic error is calculated by every measuring value of each tested flow dot ,as formulas followed : (Cubage method)
E:flowmeter error (generally total error ),two effective numbers .
Vm: flowmeter’s measuring value (displaying value).
V: after adjusted, flowmeter standard set measuring value (actual value).
It is known by basic error calculation that when Vm is larger than V, meter basic error is “+” value ,which means that meter is fast, when Vm is smaller than V , meter basic error is “—” value ,which means that meter is slow.
Flowmeter error may need to be adjusted and stay in basic error by replacing a standard gear set of the counter. That is to change mechanic transmitting ratio, which can make displaying value adjusted. Adjusting error can’t change flowmeter’s flow characters, but it can make the error curve stay in the new coordinates system.
Generally, in actual flow range, basic error of Max. and Min. tested dots is not able to surpass definitive basic error. Flowmeter used generally is tested by adjusting intrinsic gear wheel set and then adjust error again according to idiographic condition.
2.Error adjustment steps (Guide for the error adjustment table)
a. When designed, the standard gear set is 38/35. If the tested meter is found to be running faster, and causes a plus(+) error, for instance, if the error is +1.02~+0.3,replace the gear set by set 41/38(see table 1), so the error curve stays in the new coordinate system, then the error is adjusted within the error range of +0.39~-0.33.
b. During the operation of the flowmeter, the error range will be changed or overranged due to the wearing of the gear set etc. If the error range doesn’t exceed 1%, it can be adjusted within the error range, for instance, the meter error drops to -0.7+0.2, when the gear set is needed to be replaced, first check the tooth number of it, if it is 41/38, error +0.63 corresponding to it will be regarded as zero pointer (coordinate origin), then the set 41/38 will be replaced by the set 40/37. the coordinate origin of the curve shifts from zero pointer for the set 41/38 down to the +0.43 pointer for the set 40/37, so the error curve stays in the new coordinate system,