HR2 High Resistance Meter--Instructions

The two offset controls should be set correctly before the first use. Connect the two short clips included to the Shielded Sensitive Terminal and the Non-Sensitive Terminal, as shown. To “zero” the meter correctly, short the clips together, switch the center switch up to "Ohms", and turn on the meter (to any range). It should already read zero; if it does not, rotate the small recessed rotary control (in a hole in the rear of the meter) using a small screwdriver, until the display reads zero. Then it will read zero on all 9 of the ohm ranges as long as the terminals are shorted together, and will generally never need to be rezeroed. To measure > 10 G ohm accurately (or conductance < 100 pS), the “Current Offset” (knob on the edge of the meter) should also be set. Its correct position will depend slightly on temperature, and this control should be rezeroed occasionally. To set it, remove the connector from the Shielded Sensitive Terminal. (This action will minimize outside interference.) Set all 3 controls to the blue “pS” position. (Left switch = center, middle switch = down, right switch = 199.99 position. If the display is fairly stable, rotate the "Current Offset” until the average reading is zero. If the reading is not stable, see below for how to reduce external interference.

Connect the resistive sample (unknown resistance) between the "Shielded Sensitive Terminal" and the "Non-Sensitive Terminal". The short clips can be used, plugged in as shown. To measure "ohms per square", a piece of the sample no more than 3 mm wide should be prepared. Bend the clip wires so that the two clips form opposite edges of a square (with a square of the sample between the clips). For measurements away from the meter, remove the short clips and plug in the two long cables, using the red clip as the sensitive connection. To read resistance, set the middle switch to Ohms. The left switch selects the coarse range (K, M, or G ohms). K is units of a thousand, M is millions, and G is billions. The finer range selection is set with the rotary switch, which sets maximum ranges of 19.999 or 199.99 or 1999.9 (K, M, or G ohms). Select a range (of the 9 possible ranges) for best resolution. If the display reads “1 . ”, the range selected is too low; select a higher range. If the display reads zero, select a lower range. The entire readable range spans from 1 ohm to 1999.9 G ohms.

To read conductance (the inverse of resistance), set all three switches to the blue pS position. Note that the resistance in T ohms is the inverse of the conductance in pS, For example, 10 pS corresponds to 0.1 T ohms or 100 G ohms, 3 pS is 0.3333 T ohms (333.33 G ohms), 1 pS is 1000 G ohms, and 0.01 pS is 100,000 G ohms (100 T ohms), which is the highest resistance that can be distinguished from a perfect insulator using this meter. Conductance readings can be made faster than resistance readings if the sample has some capacitance. This happens because resistance readings are at constant current whereas conductance is at constant voltage (1 volt).

When doing ultra high resistance measurements, only a very small amount of current is flowing through the sample. Therefore the reading can fluctuate as a result of the operator’s movements while static electricity is present. To eliminate this interference, the meter can be set down inside a grounded conductive enclosure or high-walled "pan" made of aluminum foil. A conductive black box, which snaps onto the meter at “Case Ground”, is an available option that performs this function. External interference can also be reduced when using the long cables-- simply connect the black lead of the coaxial cable (connected to the sensitive terminal) to a metal foil enclosure that surrounds the sample. (The red lead of the coax connects to one side of the sample, while the non-coaxial lead, which is from the non-sensitive terminal, connects to the other side of the sample.) Avoid connecting either side of the sample to the metal foil. The best way to prevent interference is to plug the black box into the Case Ground jack (left of the two terminals), then set the entire meter into a metal “pan” made of aluminum foil, which should have a height of at least half its diameter, then connecting the meter to earth ground (clip onto the side screw of the black box). The metal "pan" should also be connected to ground. Each of these actions will reduce interference. When using the black box, make sure that neither terminal touches the inside of the box, which is conductive. (This type of short will not harm the meter, but an accurate reading is only possible if nothing is touching there.)

Two common effects may interfere with high resistance (and low conductance) readings. If the conductance is due to humidity, there is usually an electrochemical (battery) effect which contributes a small current. However, a small current can cause a large error if the sample resistance is high. To avoid this, make sure the clips are clean and that there are no chemical differences between one side and the other of the sample, where the clips are attached. Try reversing the connections on the sample to see if there is any difference. If there is, use the pS range and take the average of the forward and backward readings. (One of the readings could even be negative. This negative value will reduce the average, but the computed average value of conductance should nonetheless be positive.) Another effect occurs if the sample is coated with some plastic (or other insulator). If the plastic is accidentally rubbed, it will charge. As it slowly self-discharges, a small current may be generated which adds an offset to the signal. This current eventually dissipates, but it can be removed immediately by dipping the sample in water and shaking dry, or by exposing it to ac AC ionizer to discharge it.

The HR2 Meter measures resistance in 9 ranges from 19.999 K ohms to 1999.9 G ohms). Accuracy is +/-2% of the reading +/- 1 count. The 9 measurement currents are 100 micro amps down to 1 pico amp in factors of 10. The voltage applied is proportional to the displayed number; for each resistance range, the maximum displayable number (19.999, 199.99, or 1999.9) corresponds to 1.9999 volts across the sample. Therefore half scale corresponds to about 1 volt.

Measures conductance in one range: 199.99 pico siemens. Accuracy is +/-2% of reading +/- 1 count. During conductance measurements, 1 volt is applied across the component.

Battery is a standard rectangular 9 Volt type, with "LOW BATTERY" appearing on the display when approximately one hour of battery life remains. Battery life is about 50 hours using an alkaline, and 25 hours using a regular battery. A battery is included. To replace, slide off the battery back door.