# Presentation: 691235

## LPG Liquid-Measuring DevicesPart 3: Pre-Test Determinations

- NIST Weights and Measures Division
- LPG Short Course
- May 2005

## Pre-Test Determinations

- Test Liquid
- Tolerances
- Applicable requirements
- Tolerance values
- Repeatability
- Automatic Temperature Compensating System

## Test Liquid (N.1.)

- important to test with same liquid as normally dispensed through the device
- calibrate metering system & ATC for product to be used
- even variation in grade can be critical
- commercial LPG is a mixture
- composition can vary with each shipment
- coefficient of expansion may be different
- can be critical
- especially important because of differences that may exist in the tendency of the product to vaporize

## Tolerances--Overview

- devices are not capable of _**errorless**_ performance
- tolerances designed to permit measurement errors small enough not to cause serious economic hardship to the buyer or seller...yet...not so _**small**_ as to make the cost of manufacturing equipment unreasonably high
- industry often establishes more stringent requirements

## Determining Tolerances

- determine applicable tolerances
- need to know:
- length of time device has been in service
- type of test being performed
- size of test draft
- tolerances apply to device under test
- e.g., applied to meter indication, _not_ prover indication

## Types of Tests - Overview

- Normal Test (N.4.1.)
- Full flow (“fast” test)
- Also, tests at flow rate = 1⁄2 x (max rate + min rate)
- Special Test (N.4.2.)
- Slow flow (“slow” test)
- Automatic Temperature Compensating System (N.4.1.1.)
- Normal test with ATC activated
- Normal test with ATC de-activated
- Repeatability (N.4.1.2.)
- Multiple tests under same conditions

## Tolerances

- Acceptance Tolerances (G-T.1.)
- Devices just put into commercial use
- New devices tested within 30 days
- Reconditioned devices returned to service and tested within 30 days
- Devices adjusted or repaired after rejection and tested within 30 days
- Devices undergoing Type Evaluation

## Tolerances

- Maintenance Tolerance (G-T.2.)
- Applies to equipment in use except as defined under Acceptance Tolerance (G-T.1.)
- Generally, equipment in service for more than 30 days

## Tolerances

- Tolerances apply to errors of:
- Underregistration
- Meter indicates _less_ product volume than delivered and in the buyer’s favor
- Overregistration
- Meter indicates _more_ product volume than delivered and in the seller’s favor

## Tolerances – T.2., Table T.2.

- 	T.2. Tolerance Values. - The maintenance and acceptance tolerances for normal and special tests shall be as shown in Table T.2.
- 	(Amended 2003)

| Table T.2. Accuracy Classes and Tolerances for LPG and Anhydrous Ammonia Liquid-Measuring Devices  |  |  |  |  |
| --- | --- | --- | --- | --- |
| Accuracy Class  | Application  | Acceptance Tolerance
 | Maintenance Tolerance
 | Special Test Tolerance
 |
| 1.0 | Anhydrous ammonia, LPG (including vehicle tank meters)
 | 0.6 % | 1.0 % | 1.0 % |

## Sample Calculation of Tolerances

_**Example:**_**  50-gallon test draft**
- _Acceptance Tolerance:_
- Normal Test (0.6%):
- 	(0.006 x 50 gal) = 0.3 gal = +/-69.3 in3
- Special Test (1%):
- (0.01 x 50 gal) = +/- 0.5 gal = +/-115.5 in3
- _Maintenance Tolerance:_
- Normal & Special Tests (1%):
- (0.01 x 50 gal) = +/-0.5 gal = +/- 115.5 in3

## Repeatability (N.4.1.2., T.3., G-S.5.4.)

- Tests conducted at approximately same rate & draft size
- All other conditions of the test are the same
- Minimum of three consecutive drafts
- The range of tests (spread) shall not exceed 40 percent of the absolute value of the maintenance tolerance.
- Each individual test must be within applicable tolerance

## Repeatability Tolerances – Sample Calculation

**Example: 100-gallon Test Draft, Acceptance Tolerance**
- _Acceptance Tolerance_ on 100-gallon Normal Test Draft (0.6%):
- 	0.006 x 100 = 0.6 gal = +/-138.6 in3
- _Maintenance Tolerance_ on 100-gallon Normal Test Draft (1.0%):
- 	0.01 x 100 = +/-1.0 gal or +/- 231 in3
- 	_absolute value_ =
- 		remove plus & minus signs:  1.0 gal or 231 in3

## Repeatability Tolerances – Sample Calculation (cont.)

- _Repeatability Tolerance_ on 100-gal Normal Test Draft:
- 	40% of absolute value of maintenance tolerance =
- 	40% x 1.0 gal = 0.4 x 1.0 gal = 0.4 gal or 92.4 in3
- _Sample Results_ of Two 100-gallon Normal Test Drafts:
- 	_Run 1_: -100 in3			_Run 2_: +40 in3
- 			     _Total spread_: 140 in3

## Repeatability Tolerances – Sample Calculation #1 (cont.)

- Each Run
- 	Meets Acceptance Tolerance ***but***
- 	_Exceeds Repeatability Tolerance_

## Automatic TemperatureCompensating Systems (T.4., N.4.1.1.)

- One test run with ATC activated
- One test run with ATC de-activated
- Difference between results of the two tests shall not exceed:
- 1.0 percent for mechanical automatic temperature compensating systems; and
- 0.5 percent for electronic automatic temperature compensating systems
- Tests conducted at approximately same rate & draft size
- All other conditions of the test are the same
- Each individual test must be within applicable tolerance

## ATC Tolerances --Sample Calculation

- Run a 100-gallon test draft with ATC, fast flow
- Run a 100-gallon test draft without ATC, fast flow
- Electronic ATC; Maintenance Tolerance
- _Maintenance Tolerance (1%): _
- 	0.01 x 100 =1 gal  OR
- 	1 gal x 231 in3 /gal = 231 in3
- _ATC Tolerance (Electronic):_
- max difference is 0.5%

## ATC Tolerances --Sample Calculation (cont.)

- _Sample Results:_
- _with ATC_ activated:  -50 in3 		_without ATC_ activated: +90in3
- -50/231 = -0.216 gal			+90/231 = +0.390 gal
- -0.216 gal/100 gal = 			+0.390 gal/100 gal =
- percent error of -0.216%		percent error of +0.346%
_**Difference:**_  -0.216% to +0.346% = range of 0.562%
- Meets Maintenance Tolerance ***but***...
- _Exceeds Electronic ATC Tolerance_

**0**

**-0.216%**

**+0.346%**

## Pre-Test Determinations - Summary

- Test Liquid
- Same liquid as normally used with device
- Tolerances
- Set reasonable limits on device performance
- General Requirements
- Acceptance/Maintenance
- Types of Tests
- Normal Test
- Special Test
- Repeatability Test
- Automatic Temperature Compensating System Test