US 6,981,402 B2
Speed and fluid flow controller
L. Rodney Bristol, Chalfont, Pa. (US)
Assigned to Scott Technologies, Inc., Beachwood, Ohio (US)
Filed on May 30, 2003, as Appl. No. 10/452,040.
Claims priority of provisional application 60/384688, filed on May 31, 2002.
Prior Publication US 2004/0055363 A1, Mar. 25, 2004
Int. Cl. G01N 7/00 (2006.01); G01N 19/10 (2006.01)
U.S. Cl. 73—31.03 34 Claims
OG exemplary drawing
 
1. In a gas monitoring instrument having an electrically powered motor for driving a pump to bring a sample of gas from a location being tested to a sensor for determining the presence of contaminants in the gas, a motor speed control comprising:
a) a pulse modulation control and drive operatively connected between a source of voltage and the motor for controlling application of voltage drive pulses to the motor;
b) means operatively associated with the motor for sampling motor back-e.m.f. during intervals between motor drive pulses to provide an output indicative of actual motor speed;
c) means operatively connected to the means for sampling back-e.m.f. to provide a digital signal output containing information on the actual motor speed;
d) a microprocessor connected to the output of the means to provide a digital signal and connected in controlling relation to the pulse modulation control and drive for comparing the actual motor speed to a desired motor speed for controlling the operation of the pulse modulation control; and
e) means for connecting the microprocessor to the means for sampling back-e.m.f. for determining the intervals between modulated motor drive pulses during which motor back-e.m.f. is sampled.