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Instrument Configuration


Instruments may have 1 analog input and up to 10 digital inputs.   If an analog input exists then it is assumed that the digital inputs are redundant for 1 or more limits.  If the analog input is not used then the inputs may be configured as process limits or as discrete and possibly disparate signals.

Analog Input 

  • Enters the Instrument through the iVal tag.
  • Is scaled to the base units if its scaling is different from the base units scaling.
  • A Correction-Factor and zero also exists to tweak the input signal by a simple multiplier available to the operator.
  • The scaled value may also be compensated by another instrument value with a compensation formula
  • The scaled value is then put through a low pass filter and rounded to .1% of its range to improve its stability.
  • After the analog signal is scaled, compensated and filtered (Instrs[i].c.Val) it is scaled to 2 alternate units if defined (Instrs[i].c.AltVal[n]).

Digital Inputs 

  • All digital inputs are configured as active low or active high in the I/O assignments.
  • Inputs are applied to the instrument through the iIn tags (Instrs[i].c.iIn[n]).  This tag contains two signals ._In and .In where ._In is the raw input state and .In is the adjusted active input state.
  • A bit of the “Internal Input State” word (Instrs[i].c.Int.InpState.n) corresponding to the input will be set when the input is in its active state.

Rename inputs so first input is Input0

Limit Inputs

  • Inputs may be configured as process limits but are always limits when an analog signal exists.
  • A bit of the “Input State” word (Instrs[i].c.InpState.n) corresponding to the input will be set when the input is in its active state.
  • Once set the input state will remain active for a minimum of 1 second.
  • Each input will trigger its associated limit, that is Input 1 will trigger limit 1 but only if the limit is defined.
  • If an analog signal doesn’t exist then the value assigned to the limit will be used as the instrument’s value for the highest limit active.  In this way 10 limit switches could be used to estimate a tank’s level.

Disparate Inputs

  • Inputs may be configured as momentary inputs when the analog signal is not used.
  • Momentary signals will reflect the state of the actual input with a minimum active state of 1 second
  • Latched require two signals where the even number input latches and the odd unlatches the even input state tag.
  • Toggle mode toggles the Input State each time the input enters its Active State

InpState vs LmtState 

LmtState is the combine state of both the Digital and Analog values as they are applied to the defined limits.  An input will not set the associated LmtState if the limit is not defined.

InpState is the state of the associated input regardless of limits.  InpState and LmtState will be equal assuming all limits have been defined and no analog value exists.   Both InpState and LmtState represent the Active state of the input.

For Example: If a Low Level input is Active Low (i.e. a 0 signal indicates Low) then the InpState will be true when the input is false.  There is no method available to examine the actual state of the input short of going into the digital input structure and evaluating the internal _In tag.

Hold Input

The hold input is a special purpose input with a specific tag and is assigned through the other tab.

This input will cause the instrument to hold its totalizing and delta calculations and is typically used to allow a unit to be refilled while transferring by delta weight. In this case the input is likely tied to a toggle or push/pull switch.

Debug this.


The instrument configuration allows up to 3 units and scaling factures to be configured.  However, 4 scaling factors are shown because the signal itself has a raw min/max scaling factor associated with it.

  • 3 units and associated scaling factors may be configured
  • 1 unit may be configured as the primary or Limit scaling which is always the first units defined.
  • Any of the 3 units may be selected as the base units which is the units used for control and all statistical measurements.  The primary units may also be used for control if only its value is required.

Eng. Units/Pulse 

If the input is actually a counter that counts pulses off of a mass flow meter or something similar then this setting must be configured to indicate how many engineering units are represented by each pulse.   The raw signal would hold the maximum pulse count before wrapping back to 0.

Fail Safe 

This is the value to use when the input signal is faulted.


Limits are used to trigger actions and alarms based on an operator configurable setting.  Alternatively, the actions could be triggered by comparing the instruments value to some constant but limits make it easier for an operator to understand what is happening and the ability to adjust the value.

  • An instrument may have up to 10 limits
  • Limits are always entered in “Primary Units” but are scaled into all units for display
  • Each limit has a min and max range and an initial value
  • The initial value is only applied on download as long as the operator hasn’t set the value specifically
  • Each limit may be configured as low or high acting unless one of the named limits are specified.
  • A limit may trigger none or several named limits (such as Empty or Full)
  • A named limit is accessible through code as its assigned name and also used with class based configurations.
  • None-Named limits are still accessible by the given labels but only when configured as a specific instance.
  • Limits may be inherited from the instrument class


There are several ways to condition the analog inputs some of which were described with the analog input signal above (see Compensation/Calculation page for more details).

  • Compensations Instrument An instrument may be chosen to use in a compensation expression
  • Low Pass Filter A time constant may be configured as a parameter to a low pass filter
  • Debounce Debounce Timer to apply to the active state
  • Deadband Sets up a range to maintain the limit once triggered
  • Calibration Security If set requires the operator to log in before changing the calibration

Compensations Instrument 

If an instrument is chosen for compensation then it will be used as the instrument value in an associated expression.

Currently the expression is hard coded but this should be configurable.

Low Pass Filter 

A low pass filter is used to stabilize the analog signal, use 0 for no filter.  A value of 5s would indicate that a stepped value would reach 98% of its value after 5s.

NOTE: The filter is only applied to the Rate calculation


A limits active state is triggered only after a configurable debounce time (3s default) that applies equally to all limits.

What if the user wants off-going debounce and active deadbanding?  This is the case with a flow meter that triggers flow at 100 lbs/min but must kill a pump if flow stops for more than 10s.  In this case the transfer EM is looking for a flowing limit to go off to stop the pump but the specs calls for it to not stop until the flow stops for 10s.  Without making the limit low acting, the current configuration would stop the pump instantly after the flow fell below the deadband offset.  Maybe the debounce timer shouldn’t be used this way because that would put the same 10s delay on all limits which may need faster response such as a dead head situation.

The EM could be configured with a separate off delay timer rather than deferring the timing to the instrument.  Also a dead head alarm is configured separately from the limits and could be triggered of the internal limit which has no debounce timer.

In Ver 1. the debounce time was just a suggested time but a CM could override the debounce time as long as it continuously did it every scan otherwise it would go back to the configured time.  Actually this was just an initial delay when an instrument is first acquired to start looking for alarm conditions but now that is a separate object so this doesn’t apply anymore.


Once triggered a limit will remain active until the value retracts more than the deadband value (3 eng units) off the limit.  A single deadband is used for all limits.

Should deadband be entered in % like 3% of the range for example?

Calibration (formerly K-Factor) 

This is a simple calibration factor that may be used to tweak an instrument value when a full calibration isn’t available.  This value is limited between .5 to 1.5.  Note: This is not meant to replace equipment calibration.


Statistics are kept on the analog signal in base units and available for control in base units.  Since each of these requires processing time they are only calculated if configured to do so.

  • Rate1 Instantaneous Rate of Change.  Is used to estimate when a process will finished.
  • Total Total is typically used for flow meters where the flow is in units/min.  Here total is assumed the value is in per minutes.  This value is also held when the instrument is held and reset when reset.  The total has a low cutoff equal to 1% of the base unit’s range.
  • High/Low Peak Captures high and low peaks in measured values since reset
  • Delta Change in value since reset.  The delta value is always a positive value so an increasing or decreasing value will both yield positive deltas.   The delta calculation is stopped when the instrument is held and reset when the instrument is reset.
  • Run Average Running Average is based on an average of the last 30s
  • Average Average since reset

1For a flow meter the value is the rate so in this case the rate is the rate of change of the rate or the derivative; however, when the control asks for the rate on a flow instrument then it is actually checking the value of the instrument.

Resetting values 

Reset only applies to the total, delta and average. Resetting the average when acquired is an optional setting in S88 Builder Studio. The rate and running average are based on current values so don’t require reset.  Resetting occurs automatically when the controlling CM sends a reset command which occurs when the CM is acquired and thus acquires the instrument.  These values may also be reset by the operator.

However, they may also be reset with an operator reset through the instrument panel.

Change the naming on the Reset All when Acquired to Reset Average when acquired.

Add Reset Peak when acquired

Remove the option to only totalize and average while acquired to do this continuously (this feature only helps scan time but probably not enough to make it work the confusion)

Add configuration option to Track Running Average and Track Total

Add option to provide Tare function.

Rename Totalize and Average value to Track Total and Track Average



The delta has another special function in that when it is held it ignores any changes to the value and resumes were it left off once its released without accounting for the change in value.  What this does is allows a source tank to be refilled in the middle of a transfer without affecting the total amount transferred.  The trick is to get the instrument held prior to filling and releasing after it is filled.

This can be done with an animated button on the screen, with the Unit CTS button as long as the primary vessel is the vessel containing the delta instrument, or it may be a hard wired limit tied to the hold input of the instrument.


Redundancy allows multiple instruments to be associated with another such that the 3 values are combined into a single value based on selected criteria.  Analog limits combined with discrete inputs are another form of redundancy but that redundancy is fixed.




{to be determined…}


There are only a few controls for an instrument:

  • Limits Any limit may be adjust by the operator or maintenance if secured
  • Reset Resets all statistical measurements (this is not available while instrument is acquired)
  • Disable Disables the instrument so it cannot be faulted (this may be necessary for secondary instruments)
  • Zero Forces the instrument to 0 by adding an internal offset (not available for temperature)
  • Correction Factor The correction factor is used to tweak the instrument measurement by a linear multiplier based on real world observation.  If properly calibrated then this value should be 1.

Program Interface 

Instruments are typically used by End of Control CMs and CM Wrappers.  These CM interface with instruments through the instruments program interface.


  • Acquire Command to Acquire instrument (an instrument may only be acquired by 1 CM unless shared1)
  • Reset Command to reset the statistical information
  • Hold Command to hold all statistical calculations (typically used while preparing route)
  • Tare Command to set Delta value to zero prior to using it in a metering function.
  • SP Desired set point the CM is looking for from the instrument
  • SP Visible Indication from the CM that the SP should be displayed (i.e. the SP is being used)

1Instruments such as flow and level are typically exclusive use instruments because they are used to monitor 1 activity at a time but instruments such as temperature and pressure can be shared because they can be used to monitor multiple activities.  Therefore, sharing in v2 is an automatic condition based on the units selected.

Is the tare function necessary or is the same as Reset?


Because the Instrument sta


Because the instrument values require a lot of room this information will be read directly from the Instrument.

Updated on January 8, 2019

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