Field Inspection Manual — Non-Automatic Weighing Devices

Part 3, Section 26: STP-26: Weighing Systems with Multiple Load Receiving Elements

Reference

Sections 30, 31 33, 34 et 55 of the Specifications Relating to Non-automatic Weighing Devices (1998).

Purpose

A weight indicator and/or printer may be interfaced to more than one weighing element provided that the weighing system is designed to ensure accuracy of transactions, and to prevent inadvertent errors or fraud.

Two basic types of Multiple Deck Weighing Systems are used in trade:

Type 1 - a system where only one load receiving element (LRE) can be selected and operate at a time (multi-plex); and

Type 2 - a system where all load receiving elements (LREs) can operate at the same time (multi-deck). In this system each load receiving element may have its own indicating element, all indicating elements being connected to a summing weight display; or the load receiving elements are connected to a multi-channel indicating element that can display simultaneously, or in alternance, weight values from the individual load receiving elements, and can also display the sum of the weights.

Requirements

Type 1 - one Load Receiving Element operating at a time (multi-plex systems)

Diagram of a multi-plex weighing system. Two independent load receiving elements are connected to a single multi channel indicating element.

Two or more load receiving elements, designed to be used independently, are connected to a single Approved Multi Channel indicating element. This is a Multi-Plex Weighing System.

The following minimum requirements are in addition to the requirements normally applicable to vehicle scales.

  • The Multi Channel indicating element may handle up to the maximum number of load receiving elements as described in the Notice of Approval.
  • Load receiving elements may only be used separately (as shown) unless the indicating element is approved for summing separate channels (in which case the system is a Multi-Deck system and is covered in the next section - Type 2).
  • Load receiving elements must be clearly and permanently identified with the corresponding identification.
  • The indicating element must automatically provide a clear and continuous indication of which load-receiving element is in use (i.e. Scale A, Scale B, Scale C, etc.). The indication must be visible from the operator's normal position.

Note: It is preferable to identify load receiving elements as Scale A, Scale B, etc. rather than Scale 1, Scale 2. Numbers that could be confused with weight indications are not acceptable.

  • The indicating element must prohibit the use of any load receiving element that is not in use (only one load receiving element at a time).
  • The printer must provide on the ticket, for each weighing, a clear registration indicating which load receiving element was used (Scale A, Scale B , etc.).
  • When an operator-activated function (setting zero, entering a tare value, selecting or clearing a function, etc.) is performed on one particular load receiving element, functions or parameters of other load receiving elements must not be affected or altered.
  • Unless the indicating element has independent AZTMs, one for each individual load receiving element, individual Centre-of-Zero indicators (annunciators), one for each load receiving element, must be provided. Centre-of-Zero indicators must provide a continuous signal (remain active) regardless of which load receiving element is selected.
Inspection
  • Each separate load receiving element and the indicating element is considered as a complete device and must be tested accordingly.
STARS/PICASSO Coding
  • Each load receiving element shall be listed as a separate device and must be identified in some manner to prevent confusion (Scale A, Scale B, etc.). The same indicating element shall be listed for each of the load receiving elements and shall be identified as being multi-plexed. (See also STARS/PICASSO Forms Completion Manual - Device Inspection section 20).
Procedure

The purpose of this test is to ensure that when a setting is performed or a function is activated for one particular load receiving element, functions, entries or settings on the other load receiving elements are not changed or altered.

  • Zero each individual load receiving element.
  • Place a small load (e.g. 5e) on one of the load receiving elements; zero that load receiving element; verify that the zero balance condition of the other load receiving elements has not changed.
  • Enter a platter or keyboard tare for each load receiving element.
  • Clear or change the tare value on one load receiving element.
  • Verify that tare values of the other load receiving elements have not changed.
  • Place different combinations of loads on the load receiving elements; ensure that the weight are correctly and accurately indicated; ensure that the printed weights agree with indicated weights and are properly identified.
Interpretation of Results

The device complies with the requirements if:

  • keyboard entries for one load receiving element (zero, tare, etc,) or the activation of the load receiving element selection key does not alter settings or values entered (zero, tare, etc.) of the other load receiving elements;
  • the indicated and printed weights are accurate and identified as required; and
  • the device meets the installation requirements mentioned above.

Type 2 - Weighing Systems composed of several Load Receiving Elements (Multi- deck)

There are several different configurations that may be encountered. Each will have its own unique issues that must be addressed.

Scenario A
Diagram of a multi-deck weighing system. Three load receiving elements are connected to three single channel indicating elements which are connected to a computer. The computer displays each indicating element’s reading.

Two or more load receiving elements are connected to an equal number of Approved Single Channel indicating elements. This is a Multi-deck Weighing System. Output may be combined in a computer or other unapproved non-metrological indicator.

The following minimum requirements are in addition to the requirements normally applicable to vehicle scales.

  • Each individual load receiving element must be approved.
  • Each individual indicating element must be approved.
  • The individual load receiving elements must be installed adjacent to one another; they may be separated by non-sensing areas provided that there is year-round visual indication to distinguish the weighing elements and the non-sensing zone. Vehicles being weighed must still be fully scale borne.
  • The actual scale interval d and unit of measurement must the same for all means of indication in the system.
  • The total zero range of the system must not exceed 4% of the sum of the inspected capacities of the individual load receiving elements.
  • Each load receiving element must blank if the load on that element exceeds 105% of its inspected capacity.
  • Overall system capacity is equal to the sum of the inspected capacities of the load receiving elements.
  • The summing weight display must perform within applicable LOE.
  • The summing weight display must have no calibration adjustment for individual indicating elements.
  • The summing weight display must not indicate or record any weight when any one individual load receiving element exceeds 105% of its inspected capacity.
  • The summing weight display must sum any tare entries in the individual indicating elements.
  • The summing weight display must have a free floating signal used for summing the individual indicating elements.
  • The summing weight display must be in exact agreement with the sum of all the individual indicating elements.
Inspection

As per the appropriate Inspection Procedure Outline (IPO). Each deck shall be shift tested and a further shift test performed across the junction of any two adjacent decks (see also STP-15 Eccentricity Test).

STARS/PICASSO Coding

Each load receiving element and indicating element shall be listed as a separate device starting from the leftmost load receiving element as viewed from the normal operators position (in case of any uncertainty, stand facing the load receiving element on the side where the signal cable or transverse lever exits the device). Each load receiving element shall be identified as forming part of the overall multi-deck system. (see also STARS/PICASSO Forms Completion Manual - Device Inspection section 20)

Scenario B
Diagram of a multi-deck weighing system. Three load receiving elements are connected to a single multi channel indicating element.

Two or more load receiving elements are connected to a single Approved Multi Channel indicating element. This is a Multi-deck Weighing System. The Multi-channel indicating elements may handle up to the maximum number of load receiving elements as described in the Notice of Approval. Load receiving elements may only be used in combination (as shown) if the indicating element is approved for summing separate channels, or if the approved indicating element provides a separate continuous display for each of the load receiving elements.

The following minimum requirements are in addition to the requirements normally applicable to vehicle scales.

  • Each individual load receiving element must be approved.
  • The indicating element must be approved for summing separate channels, or must have separate continuous displays for each of the load receiving elements.
  • The individual load receiving elements must be installed adjacent to one another; they may be separated by non-sensing areas provided that there is year-round visual indication to distinguish the load receiving elements and the non-sensing zone. Vehicles being weighed must still be fully scale borne.
  • The actual scale interval d and unit of measurement must be the same for all means of indication in the system.
  • The total zero range of the system must not exceed 4% of the sum of the inspected capacities of the individual load receiving elements.
  • The indicating element must perform within applicable LOE.
  • The indicating element must not indicate or record any weight when any one load receiving element exceeds 105% of its inspected capacity.

Overall system capacity is equal to the sum of the inspected capacities of the load receiving elements. If any one load receiving element exceeds 105% of capacity, the entire system must blank.

Inspection

As per the appropriate Inspection Procedure Outline (IPO). Each deck shall be shift tested and a further shift test performed across the junction of any two adjacent decks. (see also STP-15 Eccentricity Test)

STARS/PICASSO Coding

Each load receiving element shall be listed as a separate device starting from the leftmost load receiving element as viewed from the normal operators position (in case of any uncertainty, stand facing the load receiving elements on the side where the signal cable or transverse lever exits the device). The same indicating element shall be listed for each of the load receiving elements and shall be identified as being multi-channel. Each load receiving element shall be identified as forming part of the overall Multi-Deck system. (see also STARS/PICASSO Forms Completion Manual - Device Inspection section 20).

Scenario C
Diagram of a weighing system that is not considered a multi-deck weighing system. Three load receiving elements are connected to a junction box which aggregates the signals and outputs the aggregate signal to a single channel indicating element.

Two or more load receiving elements are integrated through a Junction Box and the aggregate signal is output to a single channel Approved indicating element. This is not considered a Multi-deck Weighing System.

The following minimum requirements are in addition to the requirements normally applicable to vehicle scales.

  • Overall system capacity shall not exceed:
  • the capacity of the lowest capacity load receiving element in the case of all three or more section load receiving elements; and
  • one-and-one-half times (1.5 x) the capacity of the lowest capacity load receiving element in the case of all two section load receiving elements.
  • the lesser of one-and-one-half times (1.5 x) the capacity of the lowest capacity two section LRE and the capacity of the lowest capacity three or more section LRE's, in the case of mixed two and threes or more section LRE's.

Clarification:

  • a 30 000 kg three section scale and a 40 000 kg three section scale are combined into a single longer deck scale. Overall capacity is equal to 30 000 kg.
  • a 30 000 kg two section scale and a 40 000 kg two section scale are combined into a single longer deck scale. Overall capacity is equal 1.5 x 30 000 kg = 45 000 kg.
  • a 30 000 kg two section scale and a 40 000 kg three section scale are combined into a single longer deck scale. 1.5 x 30 000 kg = 45 000 kg which is larger than the capacity of the three section scale at 40 000 kg. Therefore, overall capacity is 40 000 kg.
Inspection

As per appropriate Inspection Procedure Outline (IPO). Each deck shall be shift tested and a further shift test performed across the junction of any two adjacent decks (see also STP-15 Eccentricity Test).

STARS/PICASSO Coding

Each load receiving element shall be listed as a separate device starting from the leftmost load receiving element as viewed from the normal operators position (in case of any uncertainty, stand facing the load receiving elements on the side where the signal cable or transverse lever exits the device). The indicating element shall be listed second and the remaining load receiving elements, in order, are then listed as components of the system. (see also STARS/PICASSO Forms Completion Manual - Device Inspection section 20)

Revision

Rev 1

  • clarified and added examples of the possible configurations.
  • added STARS/PICASSO coding information.
  • ensure consistent terminology for Load Receiving and Indicating Elements.
  • added inspection test criteria.
  • correct references to Specifications Relating to Non-automatic Weighing Devices (1998).
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