Eaton MTL831B Manual

Also see for MTL831B: Technical support

Contents

INM831B Rev 4 34 CONNECTIONSThe connection terminals are along the top edges of the multiplexer.These are divided into input sensor terminals (I1 to I16),excitation current source (terminals 7 & 38) and data highwayterminals (H1 and H2), as shown in Figure 5.4.1 RTD inputsThe 15 RTD inputs are split into two banks I1 to I7 and I8 toI15. The operating mode for either bank can be set (see Section 5)to:a) 2 or 4-wire modeb) 3-wire modeBecause of this, one bank could be used for 3-wire RTDs and the otherbank for 2 or 4-wire RTDs.3-wire RTDs should not be mixed with 2 or 4-wire RTDs in the samebank. The exception to this rule is when lead compensating resistorsare used with 2-wire RTDs for greater accuracy - see next page.It is important for measurement accuracy that the switches are setcorrectly for your application. Check them before operation.4.1.1 2-wire RTDs (see Figure 6)1) Connect up to 15 RTDs to terminal-pairs I1 to I15 (terminals8 to 37), making sure the polarity is correct.2) Connect a link wire between the +ve lead of each RTD (exceptthe last) and the (adjacent) –ve lead of the next RTD.3) Connect a link wire between the +ve lead of the last RTD and the+ve end of the current loop (terminal 38).4) Connect a link wire between the –ve lead of the first RTD to the–ve end of the current loop (terminal 7).5) To monitor the RTD excitation current, connect terminal 39 to 41and connect terminal 40 to 42. The unit can then calculate thecurrent from the voltage developed across the built-in 100 ohmresistor.2-wire RTD - increased measurement accuracyLead resistance in 2-wire applications causes inaccuracy. Accuracycan be increased by substituting the wire link (step 2 above) witha resistor equal in value to the resistance of the loop wiring usedto connect that RTD. The internal switch must then be set to 3-wiremode for that bank.This solution must be applied to all RTDs in thatbankFor further details see MTL publication AN9010.RTD open circuit failureThe user should be aware that any break in the excitation currentcircuit will affect all of the RTDs connected to the MTL831B.Consequently, the failure of a single RTD in the simple wiring shownbelow will cause all the other RTDs to stop operating.A solution to this problem, using signal diodes, is given in MTLpublication AN9010.Figure 5 - MTL831B terminals and their functionsI1++++++++++++++++++++-------------------- 222322I924252627I10I5I112829I1230313233I143435I1536373841I16Data highwayData highwayFigure 6 - Typical 2 wire RTD installation212019I61817I51615I41413I3121110987Spare65H2 394Spare3240H111OOR42I1++++++++++++++++++++-------------------- 222322I924252627I10I5I112829I1230313233I143435I1536373841I16212019I618171615I41413I3121110987Spare65H2 394Spare3240H111OOR42MTL 831B Analogue multiplexer transmitterMTL 831B Analogue multiplexer transmitter