Monitoring HV

[engr_joni_ee]

How do we monitor high voltage at the level of 1000 to 1200 V that we use for Photo Multiplier Tube (PMT) which don't require much current. I guess in micro-amp range. Let's say 250 micro-amp.

The ADC usually accept input from 0 to 3.3 V. How do we monitor HV ?

 

[D.A.(Tony)Stewart]

Use a linear string of cheap 250 V rated resistors or higher V ($$) in a voltage divider.

PCB area is also cost factor and dust control for creepage

<10cents vs 0.00x in volume

https://www.seielect.com/catalog/sei-rnv.pdf

 

[oscillationeer]

The photomultiplier has a negative cathode potential, right? So, buffer your ADC input
with a big current-limit meter resistor, into an inverting op amp configuration. That
allows you to diode-clamp the op amp input pin to GND without disturbing the measurement.
Something like -.001 voltage gain, will get you directly to the ADC input. Rail-to-rail
op amp or rail-to-rail with attenuator resistors (if the op amp power supply exceeds
ADC tolerance) would be suitable.

It sounds bad to use an amplifier to attenuate, but the input impedance of the ADC is
possibly low, and you need it driven (but don't want to load the HV supply).

 

[D.A.(Tony)Stewart]

The signal conditioner design depends on your specified response curves and tube design.

See Chapt. 5 https://web.archive.org/web/2014050...u.com/resources/pdf/etd/PMT_handbook_v3aE.pdf

 

[engr_joni_ee]

H2431 - 50 circuit diagram in Figure 5-13 look like a internal circuit of the PMT having dynode chain inside.

I would like to measure HV using voltage divider outside PMT. I was thinking if I chose

R1 = 2.7 Kohm
R2 = 1000 Kohm

Voltages will be across them
Vo = R1 / (R1 + R2) * 1000 = 2.69 V
Vo = R1 / (R1 + R2) * 1200 = 3.23 V

Current will run through them
I = V / R
I = 1000 / (1000 k + 2.7 k) = 0.99 mA
I = 1200 / (1000 k + 2.7 k) = 1.19 mA

How do I calculate power rating for resistors R1 and R2.

Power across R1 + R2 will be.
P = V I = 1000 x 0.99 mA = 990 mWatt
P = V I = 1200 x 1.19 mA = 1428 mWatt

 

[lenzaca99]

geometry dash world​

How do we monitor high voltage at the level of 1000 to 1200 V that we use for Photo Multiplier Tube (PMT) which don't require much current. I guess in micro-amp range. Let's say 250 micro-amp.

The ADC usually accept input from 0 to 3.3 V. How do we monitor HV ?

The classic approach is to use a high-resistance voltage divider. Choose resistors with high voltage ratings and ensure the total resistance is at least ten times the PMT's internal resistance to minimize loading effects. For example, with a 1 MΩ PMT resistance, you could use two 10 MΩ resistors in series (20 MΩ total). The voltage across the lower resistor (connected to the ADC) will be 1/20th of the HV.

 

[engr_joni_ee]

Hi lenzaca99,

You mentioned to chose the resistors with high voltage ratings. What voltage rating for the resistors do you suggest to measure the HV at the level 1000 - 1200 V ?

Regarding the total resistance to be at least ten times the PMT's internal resistance. You mean the resistors in the voltage divider should be at least ten times the PMT's internal resistance ?

Let's consider the internal resistance of PMT is 1 MΩ then how I can chose voltage divider resistors to get 3.3 V ?

 

[D.A.(Tony)Stewart]

You can use 10x 100k R's to make 1Meg each dissipating 1/10th the power and voltage stress or scale x33 to 33Meg