Engine coolant temperature sensors – a closer look

Diagnosis of engine coolant temperature gauge issue with a certain vehicle discussed ECT sensors in a specific context.

The following table of coefficients for four common sensors was derived from published measurements by TSD of a single sensor of each type.

The so-called B equation model is \(T=\frac{1}{\frac1{T_0}+\frac1Bln\frac{R}{R_0}}\).

Part R25 B25/100
AMR3321 2246 3897
ERR2081 2218 3879
ETC8946 2450 3671
AMR1425 536 4356

These are measurements of a single sample, so average values might be a little different. Additionally, the R25 / B25/100 model is only an approximation. Continue reading Engine coolant temperature sensors – a closer look

Last update: 11th April, 2021, 1:29 PM

RK2672AM – calibration

The RK2672AM is a Chinese high voltage test set. This article describes a process for calibration of the device.

This process should not be attempted unless you have the requisite competencies, experience, tools and test equipment. There are dangerous voltages involved, so assess the hazards, plan your work, don’t attempt it if fatigued or alcohol enhanced.

Above is the front panel of the RK2672AM. Continue reading RK2672AM – calibration

Last update: 16th April, 2021, 5:04 PM

Diagnosis of engine coolant temperature gauge issue with a certain vehicle

The subject vehicle is a Land Rover Defender of mixed heritage. The owner describes the engine coolant temperature (ECT) gauge as useless.

The ECT display system is a dashboard gauge and negative temperature coefficient (NTC) thermistor mounted near the engine thermostat. It measures the engine coolant temperature (hence its name) at the hottest point in the coolant circuit… so it gives the best warning that coolant might be approaching boiling point… and which point cooling capacity catastrophically falls and there is a significant risk of permanent engine damage.

It would seem that Land Rover used many different dashboard gauges, but the underlying electrical characteristics were of just two different types. Likewise there appears to be several different sensors.

The following table of coefficients for four common sensors was derived from published measurements by TSD of a single sensor of each type.

Part R25 B25/100
AMR3321 2246 3897
ERR2081 2218 3879
ETC8946 2450 3671
AMR1425 536 4356

These are measurements of a single sample, so average values might be a little different. Additionally, the R25 / B25/100 model is only an approximation. Continue reading Diagnosis of engine coolant temperature gauge issue with a certain vehicle

Last update: 11th April, 2021, 8:32 AM

A handy 230VAC 10A inline power meter based on an inexpensive module from eBay

This article describes a simple and inexpensive inline power meter for use as a test instrument.

CNC routing

The box cutouts were done on a CNC router, but they could be done with hand tools.

Above, calcs of feeds and speeds for the CNC router. The box is actually ABS, but cutting speed for Polycarbonate is the same.

Above is the tool path for one side of the box. The cutouts suit the 7P-2 strain reliefs. The gcode is generated from a custom Python file using a custom library of common shapes that I use. Continue reading A handy 230VAC 10A inline power meter based on an inexpensive module from eBay

Last update: 20th April, 2021, 6:16 PM

Comment on KN5L on balun CMRR – series through impedance fixture

In recent articles, I flagged that on some of John’s VNWA plots he showed flawed impedance calculations using VNWA’s t2s inbuilt function.

The function t2s is documented in the VNWA help.

t2s is a VNWA built in function intended to solve the so-called s21 series through fixture for impedance measurement of two terminal Zx connected between Port 1 and Port 2.

None of John’s test fixtures were equivalent to the circuit above required for valid t2s transformation. Continue reading Comment on KN5L on balun CMRR – series through impedance fixture

Last update: 1st April, 2021, 7:36 AM

Comment on KN5L on balun CMRR – two wire line example

The article Comment on KN5L on balun CMRR dealt with model and measurement of John’s coaxial choke in fixture, dealt with first because it is a simpler model. This article builds on that and models the balun wound with a pair of wires.

Above is the subject balun in fixture.

John’s schematic shows the balun as coupled coils, but that does not capture the transmission line transformation that occurs in the actual device. Again the test fixture is used without explanation. Continue reading Comment on KN5L on balun CMRR – two wire line example

Last update: 1st April, 2021, 6:46 AM

Comment on KN5L on balun CMRR – coax example

One of the ham fashions of proposed solutions to characterising a balun is to find the Common Mode Rejection Ratio (a term carried over from other applications, eg voltage driven operational amplifiers).

(Anaren 2005) explains a method of finding balun CMRR. Anaren gives a definition of CMRR:

Common Mode Rejection Ratio is defined and the ratio between the differential mode insertion loss/gain versus the common mode signal loss or gain.

Note that in a passive system, CMRR (or CMR) in dB will usually be positive, and the larger the better. You might even think that the plain English meaning of the words Common Mode Rejection Ratio would suggest that a large ratio (or high +ve dB value) would mean most rejection, goodness. Such a meaning would be quite consistent with that of CMRR (CMR) applied to operation amplifiers (for a very long time).

Anaren does not mention applying the CMRR statistic to antenna systems. I have commented elsewhere on the lack of utility of CMRR in analysing common antenna systems.

Then immediately after the above definition, they give a formula which implies the inverse:

\(CMRR=\frac{S_{1c}}{S_{1d}}\) and goodness would be a tiny fractional value, or a small (-ve) dB value.

John, KN5L, has published his own solution to balun characterisation in some online forums. Continue reading Comment on KN5L on balun CMRR – coax example

Last update: 23rd January, 2022, 3:04 PM

Baofeng BF-T1 (BF-9100) – initial impressions

I purchased two inexpensive Baofeng BF-T1 UHF portables (hand-helds) for use around the yard.

Key features:

  • LiIon pouch single cell battery that may be obtainable longer than proprietary batteries;
  • micro USB charger interface, internal charge / battery management;
  • programmable with CHIRP (channel table only);
  • chanellised operation, lockable keypad;
  • CTCSS support;
  • integrated antenna;
  • small and lightweight (110g with belt clip);
  • inexpensive.

The radio has been in the market for more than three years, so one might hope that design issues have been fixed in ‘mature’ product. Continue reading Baofeng BF-T1 (BF-9100) – initial impressions

Last update: 6th April, 2021, 12:44 PM