Temperature compensation for photomultiplier tube
An apparatus includes a sensor to generate a light signal in response to receiving gamma radiation, and a photo multiplier tube (PMT) that receives the light signal and generates a corresponding PMT signal. A voltage source provides a supply voltage to the PMT. The magnitude of the PMT signal depends on a magnitude of the supply voltage. A temperature sensor generates a temperature signal with a magnitude that varies with a temperature sensed by the temperature sensor. The temperature sensed by the temperature sensor is substantially equal to a temperature of the PMT. A signal conditioner modifies the temperature signal. A control circuit coupled between the voltage source and the signal conditioner receives the modified temperature signal and generates a control signal for adjusting the magnitude of supply voltage based on the modified temperature signal.
1 . An apparatus comprising:
a gamma sensor configured to generate a light signal in response to receiving gamma radiation;
a photo multiplier tube (PMT) in optical communication with the gamma sensor, wherein the PMT is configured to receive the light signal and generate a PMT signal in response to receiving the light signal;
a voltage source coupled to the PMT and configured to provide a supply voltage to the PMT, wherein a magnitude of the PMT signal depends on a magnitude of the supply voltage;
a temperature sensor positioned near the PMT and configured to generate a temperature signal with a magnitude that varies with a temperature sensed by the temperature sensor, wherein the temperature sensed by the temperature sensor is substantially equal to a temperature of the PMT;
a signal conditioner configured to modify a magnitude of the temperature signal to create a modified temperature signal;
a control circuit coupled between the voltage source and the signal conditioner;
wherein the control circuit is configured to receive the modified temperature signal and generate a control signal for adjusting the magnitude of supply voltage based on the modified temperature signal;
wherein the signal conditioner comprises:
a first op-amp configured as a unity gain buffer for generating a buffered temperature signal as a function of the temperature signal;
a second op-amp configured as a differential amplifier for generating the modified temperature signal as a function of the buffered temperature signal.
2 . The apparatus of claim 1 wherein the control circuit generates the control signal with a magnitude that is dependent on a magnitude of the modified temperature signal.
3 . The apparatus of claim 1 wherein the temperature signal comprises a voltage signal, and wherein the signal conditioner is configured to amplify a difference between the temperature signal and a predetermined voltage to generate the modified temperature signal.
4 . The apparatus of claim 1 wherein the temperature signal comprises a voltage signal, and wherein the signal conditioner is configured to attenuate the temperature signal.
5 . The apparatus of claim 1 wherein the magnitude of the PMT signal depends on the temperature of the PMT.
6 . The apparatus of claim 1 wherein the magnitude of the PMT signal generated by the PMT depends on a magnitude of the light signal.
7 . The apparatus of claim 1 further comprising a cylindrical housing that contains the gamma sensor, the PMT, the temperature sensor, the control circuit, the signal conditioner, and the voltage supply.
8 . The apparatus of claim 1 wherein the control circuit comprises:
a summing circuit for adding the modified temperature signal and a divided version of the supply voltage to generate an added signal;
a compare circuit for comparing the added signal to a reference voltage;
wherein the compare circuit generates the control signal in response to comparing the added signal to the reference voltage.
9 . A method comprising:
a gamma sensor generating a light signal in response to receiving gamma radiation;
a photo multiplier tube (PMT) receiving the light signal and generating a PMT signal in response to receiving the light signal;
supplying a voltage to operate the PMT, wherein a magnitude of the PMT signal depends on a magnitude of the supplied voltage;
a temperature sensor generating a temperature signal with a magnitude that depends on a temperature sensed by the temperature sensor, wherein the temperature sensed by the temperature sensor is substantially equal to a temperature of the PMT;
modifying the temperature signal;
adjusting the magnitude of supply voltage based on a magnitude of the modified temperature signal;
wherein modifying the temperature signal comprises:
a first op-amp generating a buffered temperature signal as a function of the temperature signal;
a second op-amp generating the modified temperature signal as a function of the buffered temperature signal.
10 . The method of claim 9 wherein the temperature signal comprises a voltage signal, and wherein the modified temperature signal is generated by amplifying a difference between the temperature signal and a predetermined voltage.
11 . The method of claim 9 wherein the temperature signal comprises a voltage signal, and wherein the modified temperature signal is generated by attenuating the temperature signal.
12 . The method of claim 9 wherein the magnitude of the PMT signal depends on the temperature of the PMT.
13 . The method of claim 9 wherein the magnitude of the PMT signal generated by the PMT depends on a magnitude of the light signal.
14 . An apparatus comprising:
a gamma sensor configured to generate a light signal in response to receiving gamma radiation;
a photo multiplier tube (PMT) in optical communication with the gamma sensor, wherein the PMT is configured to receive the light signal and generate a PMT signal in response to receiving the light signal;
a voltage source coupled to the PMT and configured to provide a supply voltage to the PMT, wherein a magnitude of the PMT signal depends on a magnitude of the supply voltage;
a temperature sensor positioned near the PMT and configured to generate a temperature signal with a magnitude that varies with a temperature sensed by the temperature sensor, wherein the temperature sensed by the temperature sensor is substantially equal to a temperature of the PMT;
a signal conditioner configured to modify a magnitude of the temperature signal to create a modified temperature signal;
a control circuit coupled between the voltage source and the signal conditioner;
wherein the control circuit is configured to receive the modified temperature signal and generate a control signal for adjusting the magnitude of supply voltage based on the modified temperature signal;
wherein the control circuit comprises:
a summing circuit for adding the modified temperature signal and a divided version of the supply voltage to generate an added signal;
a compare circuit for comparing the added signal to a reference voltage;
wherein the compare circuit generates the control signal in response to comparing the added signal to the reference voltage.
15 . The apparatus of claim 14 wherein the control circuit generates the control signal with a magnitude that is dependent on a magnitude of the modified temperature signal.
16 . The apparatus of claim 14 wherein the temperature signal comprises a voltage signal, and wherein the signal conditioner is configured to amplify a difference between the temperature signal and a predetermined voltage to generate the modified temperature signal.
17 . The apparatus of claim 14 wherein the temperature signal comprises a voltage signal, and wherein the signal conditioner is configured to attenuate the temperature signal.
18 . The apparatus of claim 14 wherein the magnitude of the PMT signal depends on the temperature of the PMT.
19 . The apparatus of claim 14 wherein the magnitude of the PMT signal generated by the PMT depends on a magnitude of the light signal.
20 . The apparatus of claim 14 further comprising a cylindrical housing that contains the gamma sensor, the PMT, the temperature sensor, the control circuit, the signal conditioner, and the voltage supply.
21 . The apparatus of claim 14 wherein the signal conditioner comprises:
a first op-amp configured as a unity gain buffer for generating a buffered temperature signal as a function of the temperature signal;
a second op-amp configured as a differential amplifier for generating the modified temperature signal as a function of the buffered temperature signal.
22 . The apparatus of claim 14 wherein the signal conditioner comprises:
an analog-to-digital converter for converting the temperature signal into a digital equivalent;
a data processing unit that is configured to process the digital equivalent to generate a digital equivalent of the modified temperature signal in response to the data processing unit executing instructions stored in memory, and;
a digital-to-analog converter for converting the digital equivalent of modified temperature signal into the modified temperature signal.