XTR112 datasheet error?

Hello Max,

You're correct, this issue was recently brought to our attention by another community member.  Take a look at this post for more information:

Here's a short summary:

The full equation for RG in a 2-wire RTD application is: (40/16)*(IREF*R1(R2+Rz)-2(R2*Rz))/(R2-R1).  It looks like you're correct and on the XTR112 and XTR114 tabs of the XTR_CALC.xls calculator, the equation for RG was simply copied from the XTR105 tab where the value of IREF is 0.8mA.  The equations in the product datasheet for the XTR112 and XTR114 are correct.

We're in the process of getting an updated tool online but until then, we suggest using the equations in the datasheet and/or modifying the RG and RLIN1 equations as shown below:

RG = 2.5*D14*(J12*(J11+J13)-2*J13*J11)/(J13-J12)

RLIN1 = 0.4*D13*(J13-J12)/(D14*(2*J12-J13-J11))

I double-checked a few other things in the tool and it also looks like the equation in the XTR105 tab for RLIN1 in 2-wire applications is also incorrect and should be changed to match what's shown above.  Looks like they left of the additional 2x in the denominator of the equation.

Let us know if you have any additional questions.

Hi Max,

Looks like the link I tried to point you towards is gone, not sure why.  Anyways, the paragraph I copied to this tread contained the main points of what I was trying to direct you towards.

I spent some additional time today investigating the discrepancy in values and found a few things.

First, for your XTR112 RG results I gave you the equations for a 2-wire RTD system whereas the datasheet example is for a 3-wire RTD.  The RLIN1 equation is the same for both cases, but the RG equation is slightly different between the 2-wire and 3-wire cases.  When I use the 3-wire RTD equation I get:  756.83 and for the 2-wire case I get:  774.72

That said, I went through the examples in the XTR105 and XTR112 datasheets and agree there's a discrepancy between the Excel results and the results shown in the datasheet examples.  The discrepancy seems to stem from the fact that the datasheet values for R1, R2 and Rz are slightly different than what I calculate using the common DIN IEC60751 coefficients for RTDs with an alpha of 0.00385.  The datasheet shows the values for R1, R2, and RZ as:

RZ = 60.25
R1 = 119.4
R2 = 175.84

Whereas the Excel tool calculates:

RZ = 60.26
R1 = 119.4
R2 = 175.86

When the datasheet values for RZ, R1, and R2 are plugged into the Excel tool the values for RG, RLIN1, and RLIN2 match the datasheet calculations.

I would use the Excel tool values because these are what I've used to design with these XTR products for the last several years with really good results as shown in the reference design featuring the XTR105 linked below:

I've also attached an updated XTR_Calc spreadsheet which you and other community members can use going forward instead of the one currently online.  This features the corrections for the RG, RLIN1, and RLIN2 resistor equations that you pointed out and uses the proper DIN-IEC60751 coefficients for an RTD with an alpha value of 0.00385.

xtr_calc_10-23.xlsx