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I have a component (I believe it is a thermistor, can you confirm?) de-soldered from a device. Could somebody help me identify the type of thermistor and suggest a method/procedure to identify the resistance?

photo of unknown component

Also on close examination, I found that there are two thermistors connected in series with each other. Could somebody guide me to find the values?

On one thermistor is written "151" and on other "52 56".

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  • \$\begingroup\$ What was the device? \$\endgroup\$ Commented Oct 29, 2020 at 15:06
  • \$\begingroup\$ I took this out from a Thermal Conductivity Cell \$\endgroup\$ Commented Oct 29, 2020 at 15:10
  • \$\begingroup\$ use an ohmmeter \$\endgroup\$
    – jsotola
    Commented Oct 29, 2020 at 15:14

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Those are most likely diodes or transistors. Thermistors are typically two terminals devices and are almost never connected in series (it makes it near impossible to use the stein-hart equation to find the actual temperature). On digikey there are zero thermistors available in an SOT package such as these.

Looking up the code 151 brings up a 15V zener diode PZM15NB1.

Measure across the terminals with a DMM in diode mode to get a better idea, it may be difficult but one could still probe the cutoff tips of the SOT packages.

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  • \$\begingroup\$ Thanks for the help. I took this out from a thermal conductivity cell. Are you sure that this is a SOT Package ?? I think it is an SIP package \$\endgroup\$ Commented Oct 29, 2020 at 15:26
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    \$\begingroup\$ Yeah, pretty sure its an SOT23, or similar (both devices have three terminals with middle terminals clipped off), there is a diagram here: electronics.stackexchange.com/questions/334128/… The way to identify them would be to measure them exactly with calipers. I am 99.99% sure they are not thermistors \$\endgroup\$
    – Voltage Spike
    Commented Oct 29, 2020 at 15:31
  • \$\begingroup\$ Yes, thank you so much. I measured it. It is an SOT23 Package. I will try to measure it in DMM mode and get back to you \$\endgroup\$ Commented Oct 29, 2020 at 15:55
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Possibly an RTD, such as this one.

enter image description here

Thermistors are very nonlinear and would not be preferred for heat flow measurement.

enter image description here

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  • \$\begingroup\$ Thanks for your help. I have a doubt. Can two RTD's be connected in series together as shown in the picture ? \$\endgroup\$ Commented Oct 29, 2020 at 16:10
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    \$\begingroup\$ Sure they can. Double the resistance, the same percentage change with temperature. \$\endgroup\$ Commented Oct 29, 2020 at 16:11

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