Fluid Components International FLT Series - Manual (Page 59)

Doc. No. 06EN003286 Rev. - D - 1 FLTÔ Series FlexSwitchÔ
APPENDIX D - TEMP COMP FLUID COMPONENTS INTL
Introduction
Temperature compensation (Temp Comp) is an essential part of the FLT FlexSwitch circuitry. When the Temp
Comp is set correctly, the instrument stays accurate over a process temperature range of 100°F. The instrument is
a thermal dispersion device. It relies on the temperature differential between the reference RTD, which is at the
process media temperature, and the active RTD, which is heated to produce a temperature differential (DT). For
example; with constant temperature, flow rate, process media and heater power, the DT is reduced and reaches a
stable value. If the process media temperature goes up and all other conditions stay the same, the DT is reduced.
Without Temp Comp the circuitry would process the signal as an increased flow rate.
To understand Temp Comp the output signal needs to be understood first. This temperature output signal is the
absolute voltage drop across the reference RTD, and proportional to temperature. The instrument uses this voltage
for two purposes. The voltage drop across the reference RTD is subtracted from the voltage drop across the Active
RTD to produce a voltage differential. The voltage differential is used to set flow or liquid level alarms. Also, the
voltage drop across the reference RTD adds to, or subtracts from, the output signal as a function of DT.
Note: In order to adjust the Temp Comp correctly certain parameters must be measured and calculated. All
temperature measurements should converted to degrees Fahrenheit before a temperature differential is
found. These parameters and measurements will be discussed later in this appendix.
Factory Temperature Compensation Settings
A Temp Comp adjustment procedure is performed on the instrument before it is shipped. Under normal conditions
this setting will not have to be done by the customer. However, if there have been changes in environment since
the instrument was ordered then the following instructions may need to be done by the customer.
Restoring Temp Comp Adjustments
When the control circuit is replaced or if the Temp Comp potentiometers are accidently moved the adjustments
must be restored. There are three adjustments that need to be made on the control circuit in order to set the Temp
Comp. Two of the adjustments are done with no power applied to the instrument and a third adjustment is done
with power applied. Calibration values for each instrument are on the Temp Comp calibration sheet that is found
in the plastic page protector at the back of this manual. The calibration values are listed by the serial number of
the instrument.
Equipment Required
5-1/2 digit digital multimeter (DMM). (Small clip leads are desirable.)
Adapter cable FCI part number 015664-01 for older version of the control circuit.
Flat screw driver, capable of adjusting control circuit potentiometers.
Temp Comp calibration values from the page protector in the back of this manual.
Insulating varnish or equivalent to reseal the potentiometers.
Alert: The instrument contains electrostatic discharge (ESD) sensitive devices. Use standard ESD
precautions when handling the control circuit. See Chapter 2, Installation, for ESD details.
Appendix D. Temperature Compensation