Method and apparatus for testing overfill protection devices

• US 5,485,401 A
• Filed: 06/14/1993
• Issued: 01/16/1996
• Est. Priority Date: 06/14/1993
• Status: Expired due to Term

• Current Assignee: Scully Signal Company
• Original Assignee: Scully Signal Company
• Inventors: Cadman, Gary R.
• Primary Examiner(s): Voeltz, Emanuel T.
• Assistant Examiner(s): Tran, Alan
• Application Number:
  US08/077,012
• Time in Patent Office: 946 Days
• Field of Search: 364/551.01, 364/550, 364/571.05, 340/620, 340/621, 340/624, 73/49.2 T, 73/149, 73/290 R, 73/304 R, 324/696, 324/699
• US Class Current: 702/116
• CPC Class Codes: G01F 25/20 of apparatus for measuring liquid level
• CPC Class Codes: G01F 25/24 Testing proper functioning of electronic circuits

Abstract

The present invention resides in a probe excitation and testing ("PET") system that can apply either a normal excitation or a "small" bias test excitation to overfill protection probes mounted within storage and transport tanks used to store, e.g., flammable fluids. The PET system applies the normal excitation for normal operation of the probes to provide overfill protection, and applies a "small" bias test excitation to the probes for performing diagnostic tests, including anti-cheating. The PET system can also perform a probe signature validation test under normal excitation to ascertain whether the probes are responding thereto in accordance with specifications relating to characteristic parameters of the probes'"'"' output waveforms, e.g., duty cycle, magnitude, and period.

Claims

1. A probe excitation and testing, "PET", system for an overfill protection device including a probe mounted in a tank for sensing a level of material therein, said probe operable to produce a probe output signal in response to a normal operating excitation of at least a preselected magnitude being applied thereto, said PET system comprising:

A) processor means for conducting any of a plurality of diagnostic tests and for generating an excitation control signal;

B) channel means for coupling said processor means with said probe, said diagnostic tests conducted by said processor means being able to determine whether said probe and said channel means can operate within preselected limits; and

C) excitation means coupled with said channel means and responsive to said excitation control signal for applying said normal operating excitation to provide overfill protection during filling of said tank, and for applying a bias test excitation to said probe instead of said normal operating excitation during said diagnostic test, said bias test excitation having a magnitude less than the preselected magnitude of said normal operating excitation and insufficient to power said probe to provide overfill protection yet being sufficient to conduct said diagnostic test.

2. The PET system in accordance with claim 1, wherein said excitation control signal has a preselected characteristic, and said processor means includes a first processor for generating said excitation control signal;

and a second processor for monitoring said excitation control signal and for producing an output disable signal to indicate that said excitation control signal characteristic exceeds a predetermined threshold.

3. The PET system in accordance with claim 1, wherein said processor means includes first logic means for determining whether said probe operates within predetermined limits when said normal excitation is applied thereto.

4. The PET system in accordance with claim 1, wherein said processor means includes second logic means for determining whether said probe operates within predetermined limits when said bias test excitation is applied thereto.

5. The PET system in accordance with claim 1, wherein said overfill protect on system includes a second channel, and said processor means includes third logic means for determining whether an electrical connection exists between said channel and said second channel.

6. The PET system in accordance with claim 1, wherein said overfill protection system includes a second channel, and said processor means includes fourth logic means for determining whether an unauthorized connection has been made to said second channel.

7. The PET system in accordance with claim 1, wherein said processor means includes fifth logic means for determining whether said channel has been electrically connected to a high voltage line.

8. The PET system in accordance with claim 1, wherein said processor means includes sixth logic means for determining whether said channel has been electrically connected to a ground.

9. A method of conducting a probe signature validation test in a probe excitation and testing, "PET", system for an overfill protection device, the method comprising the steps of:

A) providing a probe which, in response to a normal operating excitation of at least a predetermined magnitude, produces a probe output signal having a characteristic time-variant parameter;

B) providing a processor which generates said normal operating excitation and is responsive to signals received;

C) connecting the probe to the processor with a signal channel;

D) exciting said probe with said normal operating excitation transmitted along said channel by the processor;

E) monitoring said channel with the processor for said probe output signal resulting from said excitation to detect said characteristic time-variant parameter; and

F) testing said detected characteristic parameter to determine whether it falls within a predetermined range.

10. The method in accordance with claim 9, wherein said step of providing a probe includes providing a probe which produces a probe output signal having a plurality of characteristic parameters which include a positive half cycle amplitude, a negative half cycle amplitude, a period, and a duty cycle.

11. The method in accordance with claim 10, wherein said monitoring step includes the steps of measuring the duration of the positive half cycle of the probe output signal, the duration of the negative half cycle of the probe output signal and the amplitude of the output signal at a preselected time during each of said half cycles;

and wherein said testing step includes the steps of;

A) performing a probe period test by generating, with the processor, a period signal representing the period of the output voltage, comparing, with the processor, the period signal with preselected limits defining a range of proper period values and, if the period signal falls outside said range, generating an output of the processor indicating that said probe does not meet specifications;

B) performing a probe magnitude test by generating, with the processor, an amplitude signal representative of a high and low value of the amplitude of the output signal, comparing the amplitude signal with preselected limits stored in the processor for said high and low amplitudes, and generating an output of the processor indicating that said probe does not meet specifications concerning the amplitudes if the high amplitude represented by said amplitude signal is lower than the stored limit for said high amplitude or if the low amplitude represented by the amplitude signal is higher than the stored limit for said low amplitude; and

C) performing a probe duty cycle test by generating, with the processor, a duty cycle signal representative of the duty cycle of the output signal, comparing, with the processor, said duty cycle signal with preselected limits stored in the processor that define a range of duty-cycle values, and, if the duty cycle signal falls outside said range, generating an output signal with the processor indicating that said probe does not meet specifications.

12. A method of conducting a probe interaction test for determining channel by-pass and channel-to-channel faults in a probe excitation and testing, "PET", system for an overfill protection device, said method comprising the steps of:

A) providing a plurality of probes, each operable to produce a probe output signal in response to a normal operating excitation of at least a preselected magnitude;

B) providing connection to each probe with one of a plurality of probe channels;

C) exciting said probe channels with a test excitation having a magnitude that is less than the preselected magnitude;

D) monitoring probe responses present on the probe channels which result from the test excitation;

E) converting the monitored probe responses into a first signal representation;

F) exciting all of said probe channels with an additional test excitation except for a channel connected to a preselected probe to be tested;

G) monitoring probe responses on each probe channel generated in response to said additional test excitation;

H) converting said monitored probe responses from step (G) into a second signal representation; and

I) comparing said first and second signal representations.

13. A method of conducting an unauthorized connection test in a probe excitation and testing, "PET", system for an overfill protection device, said method comprising the steps of:

A) providing a plurality of probes, each operable to produce a probe output signal in response to a normal operating excitation of at least a preselected magnitude;

B) providing a plurality of probe channels some of which are connected to the probes and some of which are idle channels, not connected to a probe;

C) exciting said probe channels with a test excitation having a magnitude that is less than the preselected magnitude;

D) monitoring each idle probe channel for response signals present thereupon; and

E) comparing said response signals with a predetermined threshold.

14. A method of conducting an open and short circuit test in a probe excitation and testing, "PET", system for an overfill protection device, said method comprising the steps of:

A) providing a plurality of probes, each operable to produce a probe output signal in response to a normal operating excitation of at least a preselected magnitude;

B) providing connection to each probe with one of a plurality of probe channels;

C) exciting said probe channels with a test excitation having a magnitude that is less than the preselected magnitude;

D) monitoring for a probe response on each probe channel; and

E) comparing each monitored probe response with i) a first threshold level representative of a predetermined voltage;

ii) with a second threshold level representative of a short circuit; and

iii) with a third predetermined threshold level representative of an open circuit.